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Weight Gain During Pregnancy: Reexamining the Guidelines (2009)

Chapter: Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain

« Previous: Appendix D: Summary of Determinants of Gestational Weight Gain
Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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APPENDIX E
Results from the Evidence-Based Report* on Outcomes of Maternal Weight Gain

The purpose of this systematic evidence-based review, requested by the Agency for Healthcare Research and Quality (AHRQ) and conducted by the RTI International—University of North Carolina at Chapel Hill Evidence-based Practice Center (RTI-UNC EPC), was to review the evidence on outcomes of gestational weight gain with specific attention to five key questions:

  • KQ 1. What is the evidence that either total weight gain or rate of weight gain during pregnancy is associated with (1) birth outcomes, (2) infant health outcomes, and (3) maternal health outcomes? Does any evidence suggest that either total weight gain or rate of weight gain is a causal factor in infant or maternal health outcomes?

  • KQ 2. What are the confounders and effect modifiers for the association between gestational weight gain (overall and patterns) and birth outcomes? Based on the findings in KQ 1, do these confounders and effect modifiers themselves contribute to antepartum or postpartum complications or to longer-term maternal and fetal complications, including development of adult obesity?

  • KQ 3. What is the evidence that weight gains above or below thresholds defined in the 1990 IOM body mass index (BMI) guide-

*

Appendixes and evidence tables cited in this report are provided electronically at http://www.ahrq.gov/downloads/pub/evidence/pdf/admaternal/admaternalapp.pdf.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

lines or weight loss in pregnancy contribute to antepartum or postpartum complications or longer-term maternal and fetal complications? How do these relationships vary by sociodemographic characteristics (i.e., race and age)?

  • KQ 4. What are the harms or benefits of offering the same weight gain recommendations to all pregnant women, irrespective of age and body weight considerations (e.g., pregravid weight, actual body weight at a particular time point, or optimal body weight)?

  • KQ 5. What are the anthropometric tools for determining adiposity and their appropriateness for the pregnancy state? What are the risks and benefits of measuring adiposity for (1) clinical management of weight gain during pregnancy and (2) evaluation of the relationship between weight gain and outcomes of pregnancy?

The review focused on screening studies from 1990 to October 2007 that were published in English, and excluded studies with low sample size (case series < 100 and cohorts < 40) or failure to control for pregravid weight. In total, 150 studies were systematically reviewed and each was rated on quality and used to assess the strength of evidence for each outcome. The report, including appendices and evidence tables, can be accessed and viewed in its entirety at http://www.ahrq.gov/clinic/tp/admattp.htm. Literature published outside of the scope of the report (prior to 1990 and after October 2007) are reviewed in Appendix C of this report. The methods and results and of the evidence review (Chapter 3 of the report) are provided below.

CHAPTER 2:
METHODS

In this chapter, we document the procedures that the RTI International-University of North Carolina Evidence-based Practice Center (RTI-UNC EPC) used to develop this comprehensive evidence report on outcomes of maternal weight gain. The team was led by a senior health services researcher (Meera Viswanathan, PhD, Study Director), a senior epidemiologist (Anna Maria Siega-Riz, PhD, RD, Scientific Director), and a senior nurse-researcher (Merry-K Moos, FNP, MPH, co-Scientific Director).

We first describe our strategy for identifying articles relevant to our five key questions (KQs), our inclusion and exclusion criteria, and the process we used to abstract relevant information from the eligible articles and generate our evidence tables. We also discuss our criteria for grading the quality of individual articles and for rating the strength of the evidence as a whole. Finally, we explain the peer-review process.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 1. Inclusion/exclusion Criteria for Gestational Weight Gain

Category

Criteria

Study population

Women of any age with singleton pregnancies

Study settings and geography

KQ 1, KQ 2, KQ 4: Developed nations: United States, Canada, Western Europe, Japan, Australia, New Zealand

KQ 3: United States

KQ 5: All countries

Time period

January 1990 through October 2007

Publication languages

English only

Admissible evidence (study design and other criteria)

Admissible designs

Controlled trials (n ≥ 40), nonrandomized controlled trials (n ≥ 40), systematic reviews, meta-analyses, prospective trials with historical controls (n ≥ 40), prospective or retrospective observational cohort studies (n ≥ 40), and medium to large case series (n ≥ 100)

Other criteria

Original research studies must provide sufficient detail regarding methods and results to enable use and adjustment of the data and results.

Relevant outcomes must be abstractable from data presented in the papers.

Sample sizes must be appropriate for the study question addressed in the paper; single case reports or small case series (fewer than 100 subjects) are excluded.

For KQ 1, 2, 3, and 4: prepregnancy body mass index (BMI) or weight must be accounted for in the relationship between maternal weight gain and outcome.

Studies limited to women with preexisting health conditions only are excluded.

Literature Review Methods

Inclusion and Exclusion Criteria

Our inclusion and exclusion criteria are documented in Table 1. As noted in Chapter 1, this systematic review focuses on outcomes of maternal weight gain with respect to the 1990 recommendations from the Institute of Medicine (IOM). Largely for that reason, we limited our searches to articles published in 1990 and thereafter. We also restricted our searches to developed countries so that we could have data generally relevant for maternal weight gain and health outcomes in the United States.

We excluded studies that (1) were published in languages other than English (given the available time and resources); (2) did not report information pertinent to the key clinical questions; (3) had fewer than 40 subjects

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

for randomized controlled trials (RCTs) or nonrandomized cohorts with comparisons or fewer than 100 subjects for case series; and (4) were not original studies.

For KQ 1, 2, 3, and 4, we required that the reported association between maternal weight gain and health outcomes accounted for prepregnancy body mass index (BMI) or weight, either through stratified univariate analysis or multivariate analysis.

Literature Search and Retrieval Process

Databases We used multifaceted search strategies to include current and valid research on the KQs, which we applied to four standard electronic databases—MEDLINE®, Cochrane Collaboration resources, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Embase. We also hand-searched the reference lists of relevant articles to make sure that we did not miss any relevant studies. We consulted with our Technical Expert Panel (TEP) about any studies or trials that are currently under way or that may not yet be published.

Search terms. Based on the inclusion/exclusion criteria above, we generated a list of Medical Subject Heading (MeSH) search terms (Table 2 and Appendix A*). Our TEP also reviewed these terms to ensure that we were not missing any critical areas, and this list represents our collective decisions as to the MeSH terms used for all searches.

TABLE 2. MEDLINE® Search Strategy and Unduplicated Results for February 2007

Search Terms

Search Results

#2 Search “Weight Gain”[MeSH]

13,220

#5 Search pregnancy [MeSH]

577,647

#6 Search #2 AND #5

1,808

#7 Search gestational weight gain

1,725

#8 Search #6 OR #7

3,023

#9 Search #6 OR #7 Limits: English, Humans

1,696

#15 Search (“Outcome Assessment (Health Care)”[MeSH] OR “Outcome and Process Assessment (Health Care)”[MeSH] OR “Pregnancy Outcome”[MeSH]) OR “Reproductive History”[MeSH] OR “birth outcomes” OR “infant health outcomes” OR “maternal health outcomes” Limits: English, Humans

332,914

#16 Search #9 AND #15 Limits: English, Humans

474

#19 Search (“Counseling”[MeSH] OR “Directive Counseling”[MeSH])

23,091

#20 Search #9 AND #19

12

#25 Search “Body Weights and Measures”[MeSH]

279,399

#26 Search #9 AND #25

1,044

#29 Search “Anthropometry”[MeSH]

71,849

#30 Search #26 AND #29

359

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Our searches in MEDLINE® produced 715 unduplicated records. Searches in other databases yielded in 190 new records from CINAHL and 4 from Embase. Similar searches in Cochrane did not produce any new citations. Following an update on October 3, 2007, and additional searches for KQ 5, we ultimately identified 1,082 unduplicated records. In addition, peer reviews suggested 3 new citations that met our inclusion criteria.

Figure 1 presents the yield and results from our searches, which we conducted from February through October 3, 2007. Beginning with a yield

FIGURE 1. Disposition of articles for gestational weight gain.

FIGURE 1. Disposition of articles for gestational weight gain.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

of 1,085 articles, we retained 150 articles that we determined were relevant to address our KQs and met our inclusion/exclusion criteria (Table 1). We reviewed titles and abstracts of the articles against the basic inclusion criteria above; we retained relevant articles, all published after our search cutoff date of January 1990, and used them as appropriate in the discussion in Chapter 4.


Article selection process Once we had identified articles through the electronic database searches, review articles, and reference lists, we examined abstracts of articles to determine whether studies met our criteria. Each abstract was independently, dually reviewed for inclusion or exclusion, using an Abstract Review Form (Appendix B). If one reviewer concluded that the article should be included in the review, we retained it.

Of this entire group of 1,085 articles, 479 required full review. For the full article review, one team member read each article and decided whether it met our inclusion criteria, using a Full Text Inclusion/Exclusion Form (Appendix B*). Reasons for article exclusion are listed in Appendix D.

Literature Synthesis

Development of Evidence Tables and Data Abstraction Process

The senior staff who conducted this systematic review jointly developed the evidence tables. We designed the tables to provide sufficient information to enable readers to understand the studies and to determine their quality; we gave particular emphasis to essential information related to our KQs. We based the format of our evidence tables on successful designs that we have used for prior systematic reviews.

We trained abstractors by having them abstract several articles into evidence tables and then reconvening as a group to discuss the utility of the table design. The abstractors repeated this process through several iterations until they decided that the tables included the appropriate categories for gathering the information contained in the articles.

Three junior epidemiologists (Sunni Mumford, SM; Andrea Deierlein, MS, MPH; and Julie K. Knaack, MPH, RD, LDN) shared the task of initially entering information into the evidence tables. Senior staff reviewed the articles and edited all initial table entries for accuracy, completeness, and consistency. Abstractors reconciled all disagreements concerning the information reported in the evidence tables. The full research team met regularly during the article abstraction period and discussed global issues related to the data abstraction process.

The final evidence tables are presented in their entirety in Appendix C. Studies are presented in the evidence tables alphabetically by the last name

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

of the first author. A list of abbreviations and acronyms used in the tables appears at the beginning of that appendix.

Quality Rating of Individual Studies

The evidence for this systematic review is based almost entirely on observational studies. This fact presents a challenge for rating individual studies. Quality rating forms for RCTs have been validated and in use for several years; a similarly well-validated form for observational studies does not exist.

Thus, as a parallel effort, we developed a form to rate observational studies.35 This form, which can be used to rate the quality of a variety of observational studies, was based on a review of more than 90 AHRQ systematic reviews that included observational studies; we supplemented this review with other key articles identifying domains and scales.36,37 We structured the resultant form largely on the basis of the domains and subdomains suggested by Deeks and colleagues;36 we then adapted it for use in this systematic review (Appendix B*).

The form currently includes review of nine key domains: background, sample selection, specification of exposure, specification of outcome, soundness of information, followup, analysis comparability, analysis of outcome, and interpretation. Each of these domains was further evaluated on aspects of quality of the study design or reporting that would influence the reader’s perception of internal validity of the journal article (Table 3). We note that variations in reporting could result in different scores for studies drawing from the same sample.

As described in Table 3, we combined these elements to generate overall scores. We set the default as fair and then focused on the threshold required for good and poor studies; the algorithm is also described in Table 3. Fair studies, therefore, include studies that were predominantly fair (four to nine fair ratings on domains) and could not be rated either good (fewer than five good ratings for subdomains) or poor (fewer than three poor ratings for subdomains). Studies with more than five good ratings for domains that also received one or two poor ratings were downgraded to fair quality.

Key methodological concerns in this literature relate to the source of information on weight gain and the timing of measurement of weight gain. Studies that relied solely on self-reported pregravid and final pregnancy weights suffer from well-documented issues of recall bias. In addition, women tend to misreport their weight, and this bias varies by weight status38 and ethnicity.39 The timing of weight measurement (for pregravid weight and final weight) can vary depending on the design of the study; when unreported, the total weight gain during pregnancy cannot be assumed to be collected at similar time points for all women within the study,

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 3. Scoring Algorithm for Subdomains and Overall Quality Rating for Individual Studies

Definition and Scoring Algorithm

Rating

Score algorithm for background (presented in the context of previous research, hypothesis clearly described)

 

• Both elements present

Good

• Neither present

Poor

• One of two elements present

Fair

Score algorithm for sample definition (explicitly stated inclusion/exclusion criteria, uniform application of criteria, clear description of recruitment strategy, clear description of characteristics of the participants, power analysis or some other basis noted for determining the adequacy of study sample size)

 

• > Three elements present

Good

• < Two elements present

Poor

• Two or three elements present

Fair

Score algorithm for exposure (clear definition of weight gain, check for plausibility of pregravid weight, clear explanation of actions taken on outliers)

 

• All three elements present or clearly defined

Good

• Poor definition of weight gain

Poor

• Moderate or very clear definition of weight gain, one or more other elements present

Fair

Score algorithm for outcome (clear description of primary outcomes)

 

• All essential details described

Good

• Few or no essential details described

Poor

• Some essential details described

Fair

Score algorithm for soundness of information (quality of source of information on exposure, confounders, and outcome)

 

• Good for all three

Good

• Poor on source of information for exposure

Poor

• Any other score

Fair

Score algorithm for followup (adequate reporting of reasons for loss to followup)

 

• Retrospective or prospective study with clear reporting on loss to followup

Good

• Prospective study, no reporting on followup

Poor

• Retrospective study with no reporting on loss to followup

Fair

Score algorithm for analysis comparability (comparability of cohorts through design, reasonable choice of control variables, clear description of confounders, adequate adjustment for confounders)

 

• All elements present

Good

• Inadequate adjustment for confounding

Poor

• Any other score

Fair

Score algorithm for analysis outcome (withdrawals, lost to followup, and missing data adequately accounted for in the analysis, and appropriate statistical methods used)

 

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Definition and Scoring Algorithm

Rating

• Both elements clearly present

Good

• Neither element present

Poor

• Any other score

Fair

Score algorithm for interpretation (results interpreted appropriately based on study design and statistics, clinically useful, appropriate presentation, presented in the context of prior research, and conclusion supported by results)

 

• All elements clearly present

Good

• Conclusions not supported by results

Poor

• Any other score

Fair

Score algorithm for overall quality

 

• 5 or more good ratings and no poor ratings on subdomains

Good

• 3 or more poor ratings on subdomains

Poor

• < 5 good ratings and < 3 poor ratings on subdomains; 5 or more good ratings and any poor ratings

Fair

resulting in further bias. Our rating algorithm, therefore, paid special attention to the source of data on gestational weight gain and the timing of measurement. Studies that relied solely on recalled prepregnancy and total pregnancy weight were rated poor on that domain, but if they defined their gestational weight variable clearly (providing details on the timing of measurement for pregravid and final weight measurements) and either checked for the biological plausibility of pregravid weight status or explained how outliers were dealt with, they could receive an overall fair rating (assuming that they received fewer than three poor ratings overall).

Strength of Available Evidence

Our scheme follows the criteria applied in an earlier RTI-UNC EPC systematic review of systems for rating the strength of a body of evidence.40 That system has three domains: quality of the research (as evaluated by the quality rating algorithm described above), quantity of studies (including number of studies and adequacy of the sample size), and consistency of findings. Two senior staff members assigned grades by consensus.

We graded the body of literature for each KQ and present those ratings as part of the discussion in Chapter 4. The possible grades in our scheme are as follows:

  1. Strong: The evidence is from studies of sound design (good quality); results are both clinically important and consistent with minor exceptions at most; results are free from serious doubts about generalizability, bias, or

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

flaws in research design. Studies with negative results have sufficiently large samples to have adequate statistical power.

  1. Moderate: The evidence is from studies of sound design (good quality), but some uncertainty remains because of inconsistencies or concern about generalizability, bias, research design flaws, or adequate sample size. Alternatively, the evidence is consistent but derives from studies of weaker design (fair quality).

  2. Weak: The evidence is from a limited number of studies of weaker design (fair or poor quality). Studies with strong design (good quality) either have not been done or are inconclusive.

  3. No evidence: No published literature.

External Peer Review

As is customary for all evidence reports and systematic reviews done for AHRQ, the RTI-UNC EPC requested review of this report from a wide array of individual outside experts in the field, including our TEP, and from relevant professional societies and public organizations. AHRQ also requested review from its own staff. We sent 20 invitations for peer review: 6 TEP members, 6 relevant organizations, and 8 individual experts. Reviewers included clinicians (e.g., obstetrics and gynecology, women’s health/general health), representatives of federal agencies, advocacy groups, and potential users of the report.

We charged peer reviewers with commenting on the content, structure, and format of the evidence report, providing additional relevant citations, and pointing out issues related to how we had conceptualized and defined the topic and KQs. We also asked them to complete a peer review checklist. We received comments from 11 of the invited peer reviewers in addition to comments from AHRQ staff. The individuals listed in Appendix E** gave us permission to acknowledge their review of the draft. We compiled all comments and addressed each one individually, revising the text as appropriate.

CHAPTER 3:
RESULTS

This chapter presents the results of our evidence review for the following four key questions (KQs): KQ 1, outcomes of gestational weight gain; KQ 3, outcomes of gestational weight gain within or outside the recommendations of the Institute of Medicine (IOM); and KQ 5, anthropometrics of gestational weight gain.

We note that KQ 2, on modifiers of outcomes, is derivative of KQ 1. KQ 4, on recommendations for weight gain, is derivative of KQ 3. Because we framed KQ 2 and KQ4 as synthesis questions, we cover them in Chapter 4.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Appendix C provides the detailed evidence tables for KQs 1, 3, and 5. Our summary tables below feature groups of studies addressing each outcome; we present these text tables only when we have three or more studies pertaining to that particular outcome. These tables are organized by quality (good, then fair, then poor), and then alphabetically.

The summary tables generally provide information to identify the study (author and date), sample size, study quality, definition of gestational weight gain, definition of outcome, results, and confounders and effect modifiers. Unless otherwise noted, we use the metrics (e.g., grams, kilograms, pounds) that each study article used; we did not recalculate measures into the same metric.

KQ 1:
Outcomes of Gestational Weight Gain

We present outcomes in the physiological order, beginning with maternal antepartum and intrapartum outcomes, then birth outcomes (neonatal outcomes at the time of birth), infant outcomes (< 1 year), child outcomes (≥ 1 year), and finally maternal short- and long-term outcomes. Evidence Tables 1-35 (Appendix C) include studies relevant for KQ 1, listed alphabetically by author. For each outcome, we describe study characteristics and then report an overview of results, followed by detailed results. When meaningful, we present results separately for varied measures of gestational weight gain (categorical measures of weight gain, rate of weight gain, total weight gain, and other). For some bodies of evidence, variations in the definition of the outcome and inconsistencies in the direction of effect may suggest that an overall assessment of the effect is more meaningful than separate assessments of outcomes associated with each measure of gestational weight gain. Summary tables and text include information on the confounders and effect modifiers accounted for in each study.

Maternal Antepartum Outcomes
Maternal discomforts of pregnancy

Study characteristics Five studies (Evidence Table 1) investigated the relationship between weight gain and diverse maternal discomforts of pregnancy: a composite of pregnancy discomforts,41 physical energy and fatigue,42 stretch marks,43,44 and heartburn.45


Overview of results Two fair41,42 and three poor studies43-45 found no differences for women who gained an excessive amount of weight compared to those who did not, irrespective of body mass index (BMI) group,42 a higher frequency of symptoms from midpregnancy through the 36th week of gestation,46 no association between gestational weight gain

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

and heartburn in gestation,45 and some increased risk of stretch marks with increased weight gain.43,44


Detailed results A prospective cohort study in Sweden examined symptoms across pregnancy and attempted to document the prevalence and frequency of 27 pregnancy symptoms while controlling for biomedical factors.41 A cohort of 476 nulliparous women was assessed six times during gestation (gestational ages of 10, 12, 20, 28, 32, and 36 weeks). The investigators sought to determine the prevalence of various symptoms in pregnancy and to explore whether psychosocial variables are explanatory while controlling for possible confounding variables such as medical risk, smoking, and weight gain. Pregravid BMIs were calculated from self-reported weight information and women were weighed when they arrived at the hospital to give birth. Total weight gain was associated with a higher frequency of symptoms from midpregnancy through the 36th week of gestation. Reflecting on their findings, the researchers recommend that weight gain be included in future studies exploring the etiology of symptoms during pregnancy.

A secondary analysis of data collected in a US prospective cohort study investigated the relationship of prepregnancy weight and gestational weight gain on levels of physical energy and physical symptoms collected through a series of questionnaires that had been administered in patient homes in early, mid, and late pregnancy.42 All weight data were self-reported. The researchers found no differences in the number of physical symptoms or level of physical energy reported by women who gained an excessive amount of weight compared with those who did not, irrespective of BMI group. Women whose weight gain was greater than the IOM guidelines reported a lower level of functional status in the third trimester than women whose weight gain was within the guidelines (P = 0.014). Women participating in this study were 30.9 years of age on average, married, English-speaking, and of low medical risk. No confounders or effect modifiers were accounted for in the analysis.

The one study (rated poor quality) that investigated the determinants of heartburn in pregnancy undertook a cross-sectional study in the United Kingdom of 602 women of different gestational lengths who self-reported their pregravid weight and completed a questionnaire.45 The analysis, which considered age, race, parity, and pregravid BMI, found that weight gain in pregnancy was not a risk factor for heartburn in gestation.

Two studies (both rated poor quality) reported on the relationship between stretch marks (striae gravidarum) and weight gain.43,44 One was a small retrospective cohort (N = 48) recruited from one private and one teaching hospital in the United States.43 Mean total weight gain was significantly greater in women with abdominal striae than women without stretch

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

marks (P < .05) but the analysis did not account for any confounders or effect modifiers. The other study reported on a cross-sectional sample of 324 primiparous women who were assessed within 48 hours of giving birth in Great Britain.44 Logistic regression analysis found maternal age, BMI, weight gain, and neonatal birthweight to be independently associated with striae. Weight gain was a weakly significant risk factor (OR, 1.08; 95% CI, 1.02-1.14).

Hyperemesis

Study characteristics A retrospective cohort study compared the experiences of 1,270 women who had an antepartum admission before 24 weeks of gestation for hyperemesis with those of 154,821 women who experienced no antepartum admission related to vomiting (Evidence Table 2).47 Baseline weight and weight gain were abstracted from the Nova Scotia Atlee Perinatal Database, but the authors did not explain how the weights entered into the database were assessed.


Overview of results One poor study found a correlation between increasing likelihood of total gestational weight gain of < 7 kg with increasing numbers of antenatal admissions for hyperemesis.47


Detailed results The study, undertaken to determine the relationship between hyperemesis and a variety of outcomes, used the number of antenatal admissions as a marker for severity of disease. The study found a correlation between increasing likelihood of total gestational weight gain of < 7 kg with increasing numbers of antenatal admissions. Many potential confounders were incorporated into the analysis including previous pregnancy experiences, psychiatric disorders, pregravid weight, and preexisting medical diseases. Weight gain information, however, was missing for approximately 17 percent of the cohort.

Abnormal glucose metabolism

Study characteristics Eleven studies specifically investigated the relationship between weight gain in pregnancy and the development of abnormal glucose metabolism (Evidence Table 3, Table 4).3,48-57 Of these, four were done outside the United States.49,50,52,53 Numerous inconsistencies in methodology and definitions, such as differences in criteria used for the diagnosis of gestational diabetes mellitus (GDM), preclude clear summations regarding the research.

The diagnostic algorithm for assigning the diagnosis of GDM in most asymptomatic women begins with administration and interpretation of a 1-hour glucose challenge test; those women who have a glucose level following the challenge above a specified level then receive a 3-hour glucose

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 4. Gestational Weight Gain and Abnormal Glucose Control

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Kieffer et al., 200648

Pregravid weight: Self-report; if unknown calculated from wt at ≤ 10 wks gestation

Note: study aim to determine relationship of anthropometric and metabolic variables on infant outcomes

Women with GDM had significantly lower average weight gain than those without GDM but weight gain was not significantly related to glucose category

Parity, pregravid BMI, weight gain

US Michigan federally qualified community health center

1,041 Latinas

Total weight gain: Computed from last weight recorded within 7 days delivery

All BMIs

Good

Saldana et al., 20063

Pregravid weight: Self-report

 

Weight gain ratio (observed/recommended)

Race, maternal age, gestation age of weight measurement

US North Carolina prenatal study

Total weight gain: Calculated on prenatal measurement to end of second trimester

IGT OR (95% CI) 0.9 (0.7-1.1)

2,254

GDM OR (95% CI) 1.2 (0.9-1.4)

All BMIs

Good

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Edwards et al., 199655

Pregravid weight: Self-report

Pregravid wt 19.8-26.0 BMI:

G1: < 11.5 kg gain

G2: 11.6-16 kg gain

G3: > 16 kg gain

Incidence gestational diabetes:

G1: 2.3%

G2: 3.3%

G3: 2.9%

(P = .759)

Maternal age, parity, race, prenatal smoking, prenatal alcohol use, prenatal illicit drug use, pregravid health, weight and adequacy of prenatal care

US Minnesota, births at specific medical center

Total weight gain: Last prenatal assessment

1,343 divided between obese women (BMI > 29) matched to nonobese (BMI 19.8-26.0)

Pregravid wt > 29 kg

G4: lost/gained nothing

G5: 0.5-6.5 kg gain

G6: 7-11.5 kg gain

G7: 12-16 kg gain

G8: > 16 kg gain

G4: 13.3%

G5: 24.3%

G6: 11.9%

G7: 16.7%

G8: 17.3%

(P = .554)

Fair

Hackmon, et al., 200757

Pregravid weight: How determined not described

 

There was no difference in maternal weight gain during early pregnancy between patients with abnormal versus normal GCT values (mean ± SD of 4.13 ± 3.2 and 4.16 ± 1.67, respectively).

Gravidity, parity, ethnicity, BMI

US inner city population

75

Weight gain: Weight at 24-28 weeks end point for calculations

All BMIs

Fair

Kieffer et al., 200156

Pregravid weight: Self-report or, if unknown, weight assessment in 1st 10 wks gestation

Wt gain to 28 wk GA:

Multiple logistic regression analyses revealed statistically significant risk factors for GDM included increasing weight gain during first 28 wks of gestation

Age, family history diabetes, parity, BMI, weight gain first 28 weeks, ethnicity

US Detroit health care system

Latinas:

G1: < 14 lbs gain

G2: 14-28 lbs gain (reference)

G3: > 28 lbs gain

1,334 AA and Hispanic

All BMIs

Total weight gain: How determined not described

Fair

AAs:

G4: < 14 lbs gain

G5: 14-28 lbs gain

G6: > 28 lbs gain

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Murakami et al., 200552

Pregravid weight: Self-report on first visit

G1: < 8.5 kg gain

G2: 8.5-12.5 kg gain

G3: > 12.5 kg gain

AOR (95% CI) gestational diabetes

G1: 5.14 (0.97-27.20)

G2: Reference

G3: 3.91 (0.61-24.73)

Maternal age, parity, smoking, weight gain, gestational weeks; pregravid BMI

Japan hospital data

Total weight gain: Measured on admission for birth

633

All BMIs

Fair

Thorsdottir, et al., 200253

Pregravid weight: Self-report

G1: < 11.5 kg gain

G2: 11.5-16.0 kg gain

G3: 16.1-20.0 kg gain

G4: > 20 kg gain

Incidence gestational diabetes

G1: 2.9%

G2: 0

G3: 0

G4: 0

(P = .015)

Age, parity, height, gestational age

Iceland University Hospital

Total weight gain: Maternity records (no specifics offered)

615

BMI: 19.5-25.5

Fair

Bianco, et al., 199854

Pregravid weight: Self-report

Reported only for BMI > 35:

G1: weight loss or no gain

G2: 1-15 lb gain

G3: 16-25 lb gain

G4: 26-35 lb gain

G5: > 35 lb gain

Incidence GDM:

G1: 15.7%

G2: 15.0%

G3: 14.4%

G4: 13.4%

G5: 12.5%

(P = NS)

Race, parity, clinic service, substance abuse, and preexisting medical conditions

US New York

Total weight gain: Computed from measured weight within 4 weeks of delivery

Medical Center Database

11,840

Nonobese (BMI 19-27) and Morbidly obese (BMI > 35) ages 20-34

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Brennand et al., 200549

Pregravid weight: Measured weight ≤ 14 wk GA used as proxy

G1: “Low weight gain”

G2: “Acceptable weight gain”

G3: “Excessive weight gain”

Incidence GDM:

G1: 38.6%

G2: 27.3%

G3: 19.3%

(P = 0.011)

None reported

Quebec, Canada, First Nation’s People (Cree)

Total weight: Last recorded weight within 4 wks of giving birth

603

All categories per Canadian Guidelines

All BMIs ≥ 18.5

Incidence IGT:

G1: 12.0%

G2: 15.2%

G3: 7.9%

(P = 0.249)

Poor

Kabiru and Raynor, 200451

Pregravid weight: First prenatal visit

BMI < 25 first assessment:

G1: no change BMI category

G2: increase 1 category

G3: increase > 1 category

Incidence gestational diabetes

G1: 0.5%

G2: 1.5%

G3: 3.7%

(P = .005)

Pregravid weight

US Atlanta public hospital database

Total weight gain: Computed on weight at admission for birth

5,131

BMI ≥ 25 first assessment:

G4: no change BMI category

G5: increase 1 category

G6: increase > 1 category

All BMIs ≥ 20

G4: 1.0%

G5: 3.3%

G6: 1.9%

(P = .005)

Poor

Seghieri et al., 200550

Pregravid weight: How determined not described

 

Weight gain as predictor of GDM OR (95% CI)

Parity, age, pregestational BMI, weight gain, family history diabetes

Italy Outpatient Diabetes Unit

1,880

1.024 (0.974-1.077) (P = NS)

Total weight gain: How determined not described

All BMIs

Poor

AA, African American; ACOG, American College of Obstetrics and Gynecology; BMI, body mass index; CHC, community health center; CI, confidence interval; G, group; GA, gestational age; GDM, gestational diabetes mellitus; GIP, gastric inhibitory polypeptide; IGT, impaired glucose tolerance; IOM, Institute of Medicine; NS, not significant; OR, odds ratio; PNV, prenatal visit.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

tolerance test (GTT). Abnormalities in the GTT results are considered diagnostic of GDM. The set point for determining if the glucose challenge test is abnormal is not universally agreed upon. Therefore, more women in one setting may be tested for disease than in another setting, not because of an increased prevalence of disease but because of differing definitions of abnormal. In addition, impaired glucose tolerance (IGT) is not clearly defined. Women with an abnormal glucose challenge test who subsequently have a normal GTT are sometimes identified as having IGT; more commonly, women who have one abnormal value in their GTT are designated as having IGT. The lack of standardization in the criteria necessary to be considered to have IGT and GDM hampers the body of research exploring the relationship between weight gain and abnormal glucose tolerance in pregnancy. Further hampering understanding of the relationship is that GDM is generally diagnosed around 28 weeks of gestation and is treated, in part, by dietary counseling and efforts to control weight gain. Similar attention is not directed toward women without this diagnosis. Therefore, using total weight gain as a predictor of disease or as a comparison point to a population without the diagnosis is likely to result in methodologically flawed conclusions.


Overview of results Four studies (1 good,32 fair,55,56 1 poor51) found that greater weight gains in pregnancy were positively associated with abnormal glucose tolerance. Three studies (1 good quality,48 1 fair,53 1 poor49) found that women having lower than average weight gains had higher likelihood of GDM. Finally, four studies (2 poor,50,54 1 fair52,53,57) found no significant association.


Detailed results Whether total weight gain or the distribution of the gain across trimester or weeks of pregnancy predicts development of GDM is unclear from the articles we reviewed. As previously noted, treatment of the condition can alter total weight gain. Three studies3,56,57 analyzed the association between weight gain in the first two trimesters of pregnancy and the diagnosis of GDM. A good-quality study reported that a weight gain ratio at the end of the second trimester of pregnancy that was greater than the IOM recommendations correlated with abnormalities of glucose metabolism.3 A fair study found no correlation between weight gain in the first 24 to 28 weeks of gestation and an abnormal glucose challenge test, the first step in the testing process to identify GDM.57 A third study assessed to be of fair quality reported that weight gain in the first 28 weeks of gestation was a significant predictor of the diagnosis of GDM (OR, 1.02; 95% CI, 1.004-1.042; P = 0.015) for their total sample of 987 black and Latina women but that total weight gain was not.56 The OR for black women was the same (1.02; 95% CI, 1.002-1.044; P = 0.30). However, the

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

range of weight gain included in the reference category was large (14-28 pounds) especially given that nearly 50 percent of the sample entered into the reported pregnancies with BMIs > 26.0.

Overall, family history of diabetes,50,56 maternal age,3,50,56 parity,50 and BMI3,50,56,57 were found to be more predictive of abnormal glucose metabolism than gestational weight gain in the research we reviewed.

Maternal hypertensive disorder

Study characteristics Twelve studies investigated the relationship between weight gain and pregnancy-induced hypertensive disorders (Evidence Table 4, Table 5).4,25,49,51-55,58-61 Six of the studies were conducted outside the United States;49,52,53,58,59,61 six studied US cohorts.4,25,51,54,55,60 While all of these studies reported on blood pressures that became elevated during gestation, the criteria for diagnosing gestational hypertension (also called pregnancy-induced hypertension) and preeclampsia were often poorly defined; in addition, criteria for the various diagnoses lacked consistency between studies.


Overview of results The vast majority of the studies (7 fair,4,25,53,55,58-60 3 poor,49,51,61) found that increasing weight gain was associated with increasing likelihood of a pregnancy-induced hypertensive disorder. Two studies, one fair52 and one poor,54 did not support this association.


Detailed results Six studies specifically examined the impact of weight gain on the development of pregnancy-induced hypertension in women classified as obese by their pregravid weight status.4,49,54,55,58,59 A prospective cohort study from Sweden examined the relationship of weight gain by pregravid BMI on pregnancy outcomes for 245,526 women who delivered term infants between 1994 and 2002.58 When compared to a reference gain of 8-16 kg, the researchers found that gains of less than 8 kg were protective against the development of preeclampsia for all pregravid BMI categories. The finding was not significant, however, for those with BMIs < 20. Gaining more than 16 kg increased the likelihood of developing preeclampsia, especially for women who entered pregnancy with lower BMIs. The greatest increased risk was for women entering pregnancy at a BMI of 20 to 24.9 (OR, 2.31; CI, 2.15-2.49); the lowest increased risk was for women who entered pregnancy at a BMI ≥ 35 (OR, 1.50; CI, 1.17-1.92).

One US retrospective cohort study studied 771 women with BMIs of 30 or greater matched by race or ethnicity, delivery date, age categories, and parity categories with women of normal pregravid BMIs (19.8-26.0).55 For women of normal weight, as weight increased the prevalence of preeclampsia steadily increased (P = .048) but increasing weight was not associated with the prevalence of gestational hypertension. For obese women, weight

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 5. Gestational Weight Gain and Pregnancy-Induced Hypertension

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured) Total Weight Gain (How Measured)

Definition of Groups

Cedergren, 200658

Pregravid weight: Self-report; if unknown “standardized measurement” used

G1: BMI < 20

G2: BMI 20-24.9

G3: BMI 25-29.9

G4: BMI 30-34.9

G5: BMI > 35

Swedish Medical Birth Registry

245,526

Total weight gain: Computed on weight at presentation for delivery

All BMIs

Fair

DeVader et al., 200725

Pregravid weight: Noted on prenatal record or reported at postpartum stay

G1: Weight gain < 25 lbs

G2: Weight gain 25-35 lbs

G3: Gained > 35 lbs

USA Missouri, birth certificate data

94,696

Total weight gain: As stated on birth certificate data. Specifics not provided

BMI: 19.8-26.0

Fair

Edwards et al.,199655

Pregravid weight: Self-reported

Pregravid wt 19.8-26.0 BMI:

G1: < 11.5 kg gain

G2: 11.6-16 kg gain

G3: > 16 kg gain

USA Minnesota, births at specific medical center

Total weight gain: Last prenatal assessment

1,343 divided between obese women (BMI > 29) matched to nonobese (BMI 19.8-26.0)

Pregravid wt > 29 kg

G4: lost/gained nothing

G5: 0.5-6.5 kg gain

G6: 7-11.5 kg gain

G7: 12-16 kg gain

G8: > 16 kg gain

Fair

Kiel et al., 20074

Total weight gain: As stated on birth certificate data. Specifics not provided

Analysis done by each class of obesity and weight changes in gestation including: weight loss ≥ 10 lbs; weight loss 2-9 lbs; no weight change; gain 2-9 lbs; gain 10-14 lbs; gain 15-25 lbs; gain 26-35 lbs; gain > 35 lbs

USA Missouri, birth certificate data

120,251

BMIs ≥ 30.0

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

Preeclampsia by BMI for weight gain < 8 kg (reference gain 8-16 kg).

OR (95% CI):

G1: 0.90 (0.55-1.48)

G2: 0.73 (0.61-0.89)

G3: 0.64 (0.54-0.76)

G4: 0.52 (0.42-0.62)

G5: 0.63 (0.51-0.79)

Preeclampsia by BMI for weight gain > 16 kg (reference weight gain 8-16 kg): Odds ratios (95% CI)

G1: 2.23 (1.83-2.71)

G2: 2.31 (2.15-2.49)

G3: 1.88 (1.72-2.06)

G4: 1.65 (1.43-1.92)

G5: 1.50 (1.17-1.92)

Age, parity, smoking in early pregnancy, year of birth

AOR for preeclampsia (95% CI)

Maternal age, race/ethnicity, education, Medicaid status, tobacco and alcohol use, maternal height, adequacy of prenatal care, child’s sex, child’s birth year

G1: 0.56 (0.49-0.64)

G2: 1

G3: 1.88 (1.74-2.04)

 

Preeclampsia:

G1: 2.8%

G2: 2.9%

G3: 6.6%

(P = .048)

Gestational HTN:

G1: 2.3%

G2: 3.8%

G3: 3.3%

(P = .607)

Maternal age, parity, race, prenatal smoking, prenatal alcohol use, prenatal illicit drug use, pregravid health, weight and adequacy of prenatal care

G4:10.7%

G5: 7.7%

G6: 8.3%

G7: 7.9%

G8: 16.5%

(P = .076)

G4: 9.3%

G5: 8.3%

G6: 11.3%

G7: 10.3%

G8: 9.0%

(P = .832)

Data all presented in graph form:

Using a gain of 15-25 pounds as reference for each obesity class, OR of preeclampsia lower with less weight gain and higher with more weight gain

Age, education, poverty (defined as participation in one or more subsidized programs) tobacco use, parity, chronic hypertension

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured) Total Weight Gain (How Measured)

Definition of Groups

Murakami et al., 200552

Pregravid weight: Self-reported at first visit

G1: < 8.5 kg gain

G2: 8.5-12.5 kg gain

G3: > 12.5 kg gain

Japan hospital data

633

Total weight gain: Measured on admission for birth

All BMIs

Fair

Ogunyemi et al., 199860

Pregravid weight: Self-reported

G1: “low weight gain”

G2: “normal weight gain”

G3: “high weight gain”

USA, rural Alabama

582

Total weight gain: Weight at last prenatal visit

All BMIs

Fair

Thorsdottir et al., 200253

Pregravid weight: Self-reported

G1: < 11.5 kg gain

G2: 11.5-16.0 kg gain

G3: 16.1-20.0 kg gain

G4: > 20 kg gain

Iceland, university hospital

615

Total weight gain: Maternity records (no specifics offered)

BMI: 19.5-25.5

Fair

Bianco et al., 199854

Pregravid weight: Self-reported

Reported only for BMI > 35:

USA, New York Medical Center Database

G1: weight loss or no gain

G2: 1-15 lb gain

G3: 16-25 lb gain

G4: 26-35 lb gain

G5: > 35 lb gain

Total weight gain: Computed on measured weight within 4 weeks of delivery

11,840

Nonobese (BMI 19-27) and morbidly obese (BMI > 35) ages 20-34

Poor

Brennand et al., 200549

Pregravid weight: Measured weight ≤ 14 wk GA used as proxy

G1: “Low weight gain”

G2: “Acceptable weight gain”

G3: “Excessive weight gain”

Quebec, Canada, First Nation’s People (Cree)

603

Total weight gain: Computed on last recorded weight within 4 wks of giving birth

All categories per Canadian Guidelines

BMI ≥ 18.5

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

 

Confounders and Effect Modifiers Included in Analysis

Estimated OR (95% CI) preeclampsia

Maternal age, parity, smoking, weight gain, gestational weeks; pregravid BMI

G1: 0.74 (0.37-1.48)

G2: 1

G3: 0.57 (0.24-1.32)

 

Incidence preeclampsia:

G1: 10%

G2: 7%

G3: 19%

(P = < .01)

 

Age, parity, pregravid BMI, tobacco use, hypertension

% gestational HTN

G1: 1.5%

G2: 4.6%

G3: 5.1%

G4: 9.2%

(P = 0.026)

% preeclampsia

G1: 1.4%

G2: 2.3%

G3: 5.4%

G4: 4.4%

(P = 0.262)

Age, parity, height, gestational age

Incidence PIH

G1: 11.8%

G2: 13.7%

G3: 13.7%

G4: 12.4%

G5: 21.3%

 

Race, parity, clinic service, substance abuse, and preexisting medical conditions

(P = NS)

 

HTN disorders

G1: 7.3%

G2: 12.5%

G3: 19.3%

(P = 0.051)

PIH:

G1: 3.7%

G2: 6.3%

G3: 4.4%

(P = 0.698)

Preeclampsia

G1: 3.7%

G2: 6.3%

G3: 14.9%

(P = 0.013)

None reported

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured) Total Weight Gain (How Measured)

Definition of Groups

Jensen et al., 200559

Pregravid weight: Self-reported

G1: < 5 kg gain

G2: 5.0-9.9 kg gain

G3: 10.0-14.9 kg gain

G4: ≥ 15.0 kg gain

Danish medical centers

481

Total weight gain: Details not provided

BMI ≥ 30

Poor

Kabiru and Raynor, 200451

Pregravid weight: First prenatal visit

BMI < 25 first assessment:

G1: no change BMI category

G2: increase 1 category

G3: increase > 1 category

USA Atlanta, public hospital database

Total weight gain: Computed on weight at admission for birth

5,131

BMI ≥ 25 first assessment:

G4: no change BMI category

G5: increase 1 category

G6: increase > 1 category

Poor

BMI ≥ 20

Wataba et al., 200661

Total weight gain: Computed by delivery weight less pregravid weight (no details on how assessed) divided by gestational age

Separate analyses done for low, medium and high pregravid weight groups by following intervals of kg/week gain:

< 0.15:

0.15-.20; 0.20-.25; 0.25-.30; 0.30-.35; 0.35-40; > 0.40

Japanese medical center

21,718

All BMIs

Poor

AOR, adjusted odds ratio; BMI, body mass index; CI, confidence interval; G, group; GA, gestational age; HTN, hypertension; kg, kilogram; lb, pounds; NS, not significant; OGTT, oral glucose tolerance test; OR, odds ratio; PIH, pregnancy-induced hypertension; USA, United States of America; wt, weight; wts, weights.

gain and the development of either gestational hypertension or preeclampsia were not significantly associated.

In a retrospective cohort study of 603 Cree women in Canada (rated poor quality), Brennand et al.49 found that overweight and obese women had a significant unadjusted OR of 2.25 to 4.25 times higher, respectively, than normal weight women for pregnancy-induced hypertension and 1.25 to 3.45 times higher for preeclampsia.

Three retrospective cohorts were limited to women who entered pregnancy with BMIs ≥ 30.4,54,59In a study of 481 Danish women, the authors,

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

OR (95% CI) gestational HTN

G1: 1

G2: 2.1 (0.8-5.7)

G3: 3.6 (1.3-9.8)

G4: 4.8 (1.7-13.1)

(P = 0.001)

Results of 2 hour OGTT, age, pregravid BMI, gestational age, parity, smoking, ethnicity, and site of prenatal care

Incidence preeclampsia

G1: 1.9%

G2: 3.2%

G3: 1.6%

(P = .203)

Pregravid weight

G4: 2.8%

G5: 3.7%

G6: 3.7%

(P = .002)

 

No clear trends for preeclampsia or severe preeclampsia by pregravid weight status and kg/week weight gains. AOR generally crossed 1.0 or had wide confidence intervals.

 

using < 5 kg as the reference weight gain, found a statistically significant trend for development of pregnancy-associated hypertension with increasing weight (P = 0.0001).59 A U.S. study examined birth certificate data for 120,251 obese women classified according to the 1998 National Institute of Health obesity classes.4 The researchers found that the amount of weight gain associated with minimal risk for preeclampsia differed by class of obesity but that, in all classes, a gain of less than 15 pounds was protective. The third study (rated poor quality) specifically investigated pregnancy and neonatal risks associated with BMIs > 35 in 527 morbidly obese women.54

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Although these women were more likely to experience obstetrical complications than a control population (BMIs 19-27), gestational weight gain did not affect the complication rate.

One other study did not support the association between weight gain and pregnancy-induced hypertension.52 In this study, 633 Japanese women who gave birth to a singleton infant at 24-42 weeks of gestational age were studied. Pregravid BMI categories were those defined by the IOM. At the time of the study (2005) the Japan Society of Obstetrics and Gynecology did not have a recent guideline for weight gain during pregnancy; as a result, researchers used the frequency distributions from their population to set quartiles regarding weight gain and then set the parameters for insufficient and excessive gains accordingly. In this study, insufficient gain was defined as less than 8.5 kg and excessive gain as 12.5 kg. Finding no significant influence on weight gain and various perinatal outcomes of the mother or infant, the research team used other cut-off points and was still unable to find an appropriate criterion for predicting risk. The authors stated that their sample size was not sufficient to prove a lack of significance. Of note, the mean pregravid BMI of the sample was 20.9 ± 2.8 and the mean weight gain was 10.5 kg ± 3.4. While this study was assessed to be of fair quality, it has little, if any, generalizability to the United States because our population of childbearing women is more racially and ethnically diverse and have a higher mean BMI.

Gallstones

Study characteristics Two studies reported on the relationship between weight gain in pregnancy and cholelithiasis (gallstones)62,63 (Evidence Table 5).


Overview of results Two studies (1 poor62 and 1 fair63) suggest a potential relationship between weight gain and cholelithiasis.


Detailed results One study reported on weight and the development of gallstones in a prospective study of 128 northern plains Native American and white women in 2004.63 Nine independent variables including BMI, prenatal weight gain, prenatal physical activity, dietary fat, iron supplementation, age, parity, history of gallbladder disease, and serum cholesterol were analyzed. Weight assessments during pregnancy were carefully collected; how pregravid weights were determined is not specifically stated. Gestational weight gain had a nonsignificant, partial correlation of 0.09 and a beta coefficient of 0.13. A case-control study (rated poor quality), using data abstracted from birth certificates, reported on 6,211 women from the state of Washington who had a gallstone-related diagnosis at delivery or in the first year postpartum between 1987 and 2001.62 Four controls

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

were randomly selected for each case and matched for year of delivery. Multiple logistic regression found an inverse relationship between gestational weight gain and gallbladder disease. The OR per kg was. 0.98 (95% CI, 0.97-0.99; P = < 0.001). Maternal age, race, BMI based on self-reported pregravid weight, GDM, and infant gestational age were accounted for in the analysis.

Maternal Intrapartum Outcomes
Premature rupture of membranes (PROM)

Study characteristics Investigators explored the relationship of gestational weight gain and the risks for premature rupture of membranes (PROM) in two studies (Evidence Table 6).64,65 One involved a total of 1,176 women who had experienced preterm delivery, defined as gestation ≤ 36 weeks, with PROM (n = 220), preterm delivery without PROM (n = 184), full-term delivery with PROM, defined as gestation ≥ 37 weeks, with at least 3 hours of PROM before the onset of labor, (n = 184), and 588 controls. Women were recruited following delivery at two academic medical centers in the United States.64 In another study,65 the investigators analyzed data for 62,167 women enrolled in the Danish National Birth Cohort who had pregravid weight and total weight gain recorded in the registry. They assessed the impact of obesity and gestational weight gain on the risk of various subtypes of preterm birth, including PROM. Pregravid weight and gestational gains were self-reported.


Overview of results Two fair studies64,65 suggest that low weight gain (< 21 pounds) or low rate of weight gain (< 275 g per week) is associated with a higher risk of PROM for full-term pregnancies and preterm pregnancies.

Results for categorical measures of weight gain. A retrospective case-control study,64 published in 1992, found that weight gain below the reference category of 21 pounds to 30 pounds significantly increased the risk of preterm delivery with PROM while weight gain above the reference category significantly reduced the risk of PROM. Similar trends were noted for full-term PROM. However, they were statistically significant only for gestational weight gain of 31 to 40 pounds when compared with women who gained 21 to 30 pounds (OR, 0.56; 95% CI, 0.33-0.94). Many potential confounders and effect modifiers were included in the analyses, including diet quality, BMI, age, race, parity, gestational iron supplementation, various medical conditions such as chlamydia that are considered risks for PROM, and smoking. The authors did not say if they adjusted for gestational age as a continuous variable. All variables, including pregravid

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

weight and total weight gain, were assessed through a questionnaire administered to most of the subjects within 72 hours of giving birth.


Results for rate of weight gain In the Danish cohort study, women with a weekly weight gain of less than 275 grams per week had an adjusted hazards ratio for PROM of 1.5 (95% CI, 1.2-1.7) compared with women gaining between 276 grams and 675 grams weekly. When compared with women with BMIs of 18.5 to 24.9, those with either low (< 18.5) or high (> 30) BMIs had significantly higher rates of preterm delivery with PROM. The authors adjusted for prepregnancy BMI, weight gain, parity, mother’s age, socio-occupational status, and lifestyle exposures in early pregnancy including smoking and alcohol exposure.65

Preterm labor

Study characteristics One poor study (Evidence Table 7) examined the relationship between gestational weight gain and preterm labor.66 Preterm labor was not defined. This study, set in the United States, examined data from 11,505 women at the Boston Hospital for Women. The study defined gestational weight gain as pounds gained per week (≤ 0.4, 0.41 to 0.65, 0.66 to 0.9, and > 0.9).


Overview of results One poor study suggested that weight gain below 0.65 to 0.9 pounds per week significantly increased the risk of preterm labor.66


Results After controlling for an extensive list of confounders and effect modifiers (race, height, prepregnancy weight, infant sex, maternal age, education, health insurance, marital status, planned pregnancy, parity, previous induced or spontaneous abortion, previous stillbirth, uterine exposure to diethylstilbestrol, incompetent cervix, uterine anomaly, maternal morbidity, substance abuse, caffeine use, and prenatal care), the study found that weight below the reference range of 0.66 to 0.9 pounds per week significantly increased the risk of premature labor (AOR for 0.41-0.65 pounds per week: 1.7, 95% CI, 1.3-2.1; AOR for ≥ 0.4 pounds per week: 3.0; 95% CI, 2.2-4.2). Weight gain above 0.9 pounds per week did not have a significant effect on premature labor.

Postterm pregnancy

Study characteristics One study58 used data from 245,526 pregnancies identified through the Swedish Medical Birth Registry (Evidence Table 8).


Overview of results One fair study found no evidence of association between gestational weight gain and postterm gestation.58

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results The author examined the effects of low (< 8 kg) and high weight gain (> 16 kg), compared with the effect of average weight gain (8-16 kg), on deliveries at > 41 weeks of gestation across strata of maternal pregravid BMI strata. After adjusting estimates for maternal age, parity, smoking in early pregnancy, and year of birth, no significant associations emerged between gestational weight gain and postterm gestational age. The study suggests that low or high gestational weight gain has no effect on postterm gestation.

Induction of labor

Study characteristics Five studies examined the relationship between gestational weight gain and labor induction (Table 6, Evidence Table 9) Of these, three were set in the United States,25,51,67 one in Denmark,59 and one in Finland.68 Of these five studies, three were of poor quality.51,59,68 Three examined induction of labor59,67,68 and two examined failed induction of labor (defined as a birth that required a cesarean delivery despite induction of labor).25,51 One of five studies was limited to obese, glucose-tolerant women,67 and one to women of normal weight;25 the other studies included women with a range of pregravid BMI. Each of the five studies defined gestational weight gain differently. Three used categories of gestational weight gain, with different cutpoints.25,59,67 One stratified its sample by weight gain categories, comparing women with normal prepregnancy weight and weight gain during pregnancy with those with abnormal weight gain during pregnancy, defined as ≥ 20 kg or ≤ 5 kg during pregnancy; the study did not specify the prepregnancy weight status of women in these “abnormal” weight gain categories.68 Another study characterized weight gain as change in BMI class between prepregnancy weight and weight at delivery.51 The study defined BMI categories as follows: normal, BMI 20 to 24.9; overweight, BMI 25 to 29.9; obese I, BMI 30 to 34.9; obese II, BMI 35 to 39.9; morbid obesity, BMI ≥ 40.51.


Overview of results Two fair25,67 and three poor51,59,68 studies examined the association of increased gestational weight gain and labor induction59,67,68 or failure of labor induction,25,51 and found a risk of labor induction or failure of induction with increased gestational weight gain.


Results The three studies that looked at induction of labor found a statistically significant increase in the risk of labor induction with increases in gestational weight gain.59,67,68 The magnitude of the effect across all three studies cannot be summarized because of differences in the definition of weight gain and in the nature of confounders controlled for in the analysis. Both studies examining failed induction of labor found a significant as-

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 6. Gestational Weight Gain and Induction of Labor

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured) Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

DeVader et al., 200725

Pregravid weight: Medical record: If missing, obtained from mother during postpartum hospital stay

Total weight gain: Obstetrical records

G1: < 30 lbs

G2: 30-35 lbs

G3: > 35 lbs

AOR for failed induction of labor vs. other birth outcomes

G1: 0.68

(95% CI, 0.59-0.78)

G2: 1.0

G3: 1.51

(95% CI, 1.39-1.64)

Maternal age, maternal race or ethnicity, maternal education, Medicaid status, tobacco use, alcohol use, maternal height, prior pregnancy, adequacy of prenatal care, child’s sex, and child’s birth year

USA, birth certificate data

94,696

Normal weight only

Fair

Graves et al., 200667

Pregravid weight: Actual prepregnant weight or early first trimester weight documented in medical records

Total weight gain: Last prenatal assessment

≤ 45 pounds vs. > 45 pounds

OR induction of labor for > 45 lb: 1.5 (95% CI, 1.0-2.4)

Maternal BMI, infant birthweight, and gestational age at delivery

USA, midwifery practices

1,500

All weights/BMI

Fair

Ekblad and Grenman, 199268

Pregravid weight: Data from records, unclear if self-reported

Total weight gain: Last prenatal assessment

G1: weight gain ≤ 5 kg

G2: weight gain ≥ 20 kg

G3: reference (normal prepregnancy weight and normal weight gain [undefined])

Percentage induced

G1: 23%

G2: 43%

G3: 24

P < 0.05 for G2 vs. G3

NA

Finland, hospital

357

Normal weight only

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Jensen et al., 200559

Pregravid weight: Records or self-report of pregravid BMI Total weight gain: Last prenatal assessment

G1: < 5.0 kg

G2: GWG 5.0-9.9 kg

G3: GWG 10.0-14.9 kg

G4: GWG ≥ 15 kg

OR for induction of labor

G1: 1.0

G2: 2.7

(95% CI, 1.3-5.7)

G3: 2.8

(95% CI, 1.3-5.9)

G4: 3.7

(95% CI, 1.7-8.0)

P for trend = 0.002

Age, pregravid BMI, 2 hour OGTT result, smoking, gestational age

Denmark, university hospitals

481

Obese only

Poor

Kabiru and Raynor, 200451

Pregravid weight: Weight at first prenatal visit

Total weight gain: Weight at admission for birth

G1: normal BMI, no change in BMI between first prenatal visit and delivery

G2: normal BMI, 1 category increase in BMI between first prenatal visit and delivery

G3: normal BMI, > 1 category increase in BMI between first prenatal visit and delivery

G4: overweight BMI, no change in BMI between first prenatal visit and delivery

G5: overweight BMI, 1 category increase in BMI between first prenatal visit and delivery

G6: overweight BMI, > 1 category increase in BMI between first prenatal visit and delivery

Percent failed induction of labor

G1: 4.7

G2: 9.2

G3: 15.9

P < 0.001

NA

USA, hospital

5,131

All BMIs > 20

Poor

G4: 7.9

G5: 10.3

G6: 14.6

P < 0.001

AOR, adjusted odds ratio; BMI, body mass index; G, group; GWG: gestational weight gain; OGTT, oral glucose tolerance test.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

sociation between gestational weight gain and increase in the risk of failed induction compared with all other delivery routes.25,51

Length of labor

Study characteristics Three cohort studies, set in Finland and the United States, examined the association between gestational weight gain and labor (Table 7, Evidence Table 10).68-70 Two studies focused on length of labor,68,69 one on labor abnormalities.70 The definition of gestational weight gain differed across studies. One study examined an overall increase in weight of > 25 percent or ≤ 25 percent for women with normal pregravid weight (90-120 percent of normal weight for height based on Metropolitan Life Insurance Company Table for 1983).69 Another reported on categories of gestational weight gain (< 16 pounds, 16-25 pounds, 26-35 pounds, and > 35 pounds) for pregravid BMI categories defined by the IOM.70 The third study, of poor quality, stratified its sample by weight gain categories, comparing women with normal prepregnancy weight and weight gain during pregnancy with those with abnormal weight gain (≥ 20 kg, or ≤ 5 kg) during pregnancy; the study did not specify the prepregnancy weight status of women in these “abnormal” weight gain categories.68


Overview of results Two of three studies (2 fair,69,70 1 poor68) suggested that higher weight gain among normal weight women of normal weight was associated with longer labor.68,69


Results The two studies that examined length of labor demonstrated significantly longer second stage of labor for women with high weight gain, based on samples of 35,768 and 10,469 respectively. Neither study controlled for confounders or effect modifiers.

The study that reported on labor abnormalities found higher odds of labor abnormalities for women gaining > 35 pounds compared with women gaining < 16 pounds. These odds lost statistical significance when adjusted for confounders. In a trend analysis, the study found a higher risk of labor abnormalities with increased weight gain, suggesting that a difference of 10 pounds corresponds to an OR of 2 (P < 0.0001) after adjusting for BMI, patient care (private vs. nonprivate), parity, infant sex, hypertension, and macrosomia.70

Mode of delivery

Study characteristics Twenty-one cohort studies reported on the relationship between gestational weight gain and mode of delivery (Table 8, Evidence Table 11).4,25,49,51,52,54,58,59,61,67-78 Thirteen studies were set in the United States,4,25,51,54,67,69-71,73-77 three in Canada,49,53,72,78 two in Ja-pan,52,61 one in Sweden,58 one in Denmark,59 and one in Finland.68

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 7. Gestational Weight Gain and Length of Labor

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Johnson et al., 199270

Pregravid weight: Self-report collected at first antepartal visit

G1: total weight gain < 16 pounds

G2: total weight gain 16-25 pounds

G3: total weight gain 26-35 pounds

G4: total weight gain > 35 pounds

Elevated odds of labor abnormalities only in the group gaining > 35 pounds compared with women gaining < 16 pounds; not significant when adjusted for confounders

Prepregnancy weight quartile, height (tertile), BMI category, race/ethnicity, marital status, private physician, parity, infant sex, maternal age, hypertension, and birthweight

USA, prenatal clinics

3,191

Total weight gain: Last prenatal visit

All weights/BMI

Trend analysis showed risk of labor abnormalities with increased weight gain, a difference in 10 lb. corresponds to OR = 2 (P < 0.0001) after adjusting for BMI, patient care (private vs. nonprivate), parity, infant sex, hypertension, and macrosomia

Fair

Purfield and Morin, 199469

Pregravid weight: Self-report as noted in medical chart

G1: prepregnant weight increased by 25% or less

G2: prepregnant weight increased by more than 25%

Normal weight primigravidas with a low risk pregnancy who gained an excessive amount of weight had a longer mean length of second stage labor than women who gained less weight

NA

USA, Tertiary care medical center

Total weight gain: Weight at admission to hospital for birth

104

Minutes of length of second stage in minutes by weight groups (SD):

G1: 72.42 (46.69)

G2: 93.28 (52.87)

t = −2.05 P = 0.02

Normal weight women only

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Ekblad and Grenman, 199268

Pregravid weight: Data from records, unclear if self-reported

G1: weight gain ≤ 5 kg

G2: weight gain ≥ 20 kg

G3: reference (normal prepregnancy weight and normal weight gain [undefined])

Labor pattern-I stage (minutes ± SD)

G1: 333 ± 208

G2: 374 ± 208

G3: 346 ± 188

NA

Finland, hospital

357

Labor pattern-II stage (minutes)

G1: 15 ± 18) P < 0.05 compared to reference category

G2: 27 ± 25

G3: 21 ± 18

Labor pattern-III stage (minutes)

G1: 13 ± 13

G2: 13 ± 11

G3: 12 ± 12

Total weight gain: Last clinically measured weight prior to delivery

Normal weight only

Poor

BMI, body mass index; G, group; SD, standard deviation.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

All 21 studies examined cesarean delivery as an outcome. Five examined instrumental delivery in addition to cesarean delivery.25,51,58,68,69 Eight studies reported on cesarean delivery without providing further definition.4,25,49,54,58,59,74,76 The studies that offered some detail varied in their definition; these studies defined cesarean delivery as failure to progress,51 unscheduled cesarean,67,70 cesarean including elective and emergency,52 elective cesarean and emergency cesarean,61,68 cephalopelvic disproportion/failure to progress, fetal distress, breech, and other indications,73 cesarean delivery for cephalic presentation,77 and cesarean delivery for singleton cephalic presentation separately analyzed for primary and repeat cesareans, with and without labor.78 A key consideration in assessing the risk of cesarean delivery is the route of previous delivery; with the declining prevalence of vaginal birth after cesarean (VBAC), a history of prior cesarean delivery is likely to result in cesareans for all subsequent pregnancies. Studies that fail to account for prior route of delivery cannot therefore control for its confounding effect. Eleven studies did not take into account prior route of delivery.4,25,49,52,54,58,59,61,67,68,70

Definitions of gestational weight gain also varied greatly. Some studies used categorical definitions designed to identify high weight gain alone,67,71 weight gain across a spectrum of gain,4,25,49,52,54,58,59,70,72,74,77 continuous weight gain,73,76 rate of weight gain,61,78 and weight gain in relation to pregravid weight.51,68,69,75


Overview of results Across the 14 fair4,25,52,58,67,69-73,75-78 and 7 poor49,51,54,59,61,68,74 studies that examined gestational weight gain as a predictor of route of delivery, only four (2 poor) failed to show an effect of gestational weight gain on route of delivery.49,52,54,67 The remainder demonstrated higher risks of cesarean delivery associated with gestational weight gain, with some evidence suggesting more pronounced risks associated with high pregravid BMI status. Notably, only 10 studies controlled for route of previous delivery. Of these, five controlled for co-morbidities that could have been significant confounders for route of delivery.71,72,75,76,78 One study explicitly examined the interactions between weight gain and pregravid weight; it did not find any significant effect.77

Results across BMI categories for categorical measures of weight gain. Fifteen studies considered weight gain across a range of pregravid weight categories. Of these, two fair studies defined gestational weight gain as a categorical variable (≤ 45 pounds vs. > 45 pounds,67 and < 41 vs. ≥ 41 pounds71). One of these two studies, limited to primary cesarean, found a significant association between weight gain and cesarean delivery (AOR, 1.38; 95% CI, 1.34-1.41).71 This study found pregravid BMI, diabetes, and hypertension to also be strong predictors of cesarean delivery. The other,

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 8. Gestational Weight Gain and Mode of Delivery

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Cedergren, 200658

Pregravid weight: Self-report; if unknown, standardized measurement is made during first visit to maternity health care center

Weight gain < 8 kg, 8-16 kg, and > 16 kg for each BMI class below

Sweden, Medical Birth Registry

245,526

G1: BMI < 20

G2: BMI 20-24.9

G3: BMI 25-29.9

G4: BMI 30-34.9

G5: BMI ≥ 35

All weights/BMI

Total weight gain: Measured when woman entered delivery unit

Fair

Chen et al., 200473

Pregravid weight: Weight taken at first prenatal visit if presented before 20 weeks; if after 20 weeks, self report

Gestational weight gain in lbs

USA, private practice

3,355

All weights/BMI

Fair

Total weight gain: Last clinically measured weight prior to delivery

DeVader et al., 200725

Pregravid weight: Medical record; if missing, obtained from mother during postpartum hospital stay

G1: < 30 lbs

G2: 30-35 lbs

G3: > 35 lbs

USA, birth certificate data

94,696

Normal weight only

Fair

Total weight gain: Obstetrical records

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

AOR for weight gain < 8 kg for cesarean section compared with weight gain

8-16 kg (95% CI)

G1: 1.07 (0.89-1.29)

G2: 0.98 (0.92-1.05)

G3: 0.88 (0.82-0.95)

G4: 0.81 (0.73-0.90)

G5: 0.75 (0.66-0.87)

AOR for weight gain < 8 kg for instrumental delivery compared with weight gain

8-16 kg (95% CI)

G1: 0.89 (0.71-1.11)

G2: 0.88 (0.80-0.96)

G3: 0.85 (0.76-0.95)

G4: 0.75 (0.63-0.88)

G5: 0.83 (0.65-1.03)

Maternal age, parity, smoking in early pregnancy, and year of birth

AOR for weight gain > 16 kg for cesarean section compared with weight gain

8-16 kg (95% CI)

G1: 1.29 (1.17-1.43)

G2: 1.24 (1.19-1.29)

G3: 1.23 (1.17-1.30)

G4: 1.22 (1.10-1.35)

G5: 1.27 (1.05-1.52)

AOR for weight gain > 16 kg for instrumental delivery compared with weight gain 8-16 kg (95% CI)

G1: 1.28 (1.15-1.43)

G2: 1.19 (1.14-1.25)

G3: 1.14 (1.06-1.23)

G4: 1.09 (0.93-1.27)

G5: 1.04 (0.77-1.40)

Progression of AOR of cesarean delivery weight gain (for every 5 lbs): 1.094 (1.074-1.115)

BMI, maternal height, maternal age, pregnancy weight gain, gestational age at delivery, and fetal birthweight

AOR for cesarean (95% CI):

G1: 0.82 (0.78-0.87)

G2: 1.0

G3: 1.35 (1.29-1.40)

Maternal age, maternal race or ethnicity, maternal education, Medicaid status, tobacco use, alcohol use, maternal height, prior pregnancy, adequacy of prenatal care, child’s sex, and child’s birth year

AOR for instrumental (95% CI): G1: 0.97 (0.90-1.04)

G2: 1.0

G3: 1.03 (0.97-1.08)

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Graves et al., 200667

Pregravid weight: Actual prepregnant weight or early first trimester weight documented in medical records

≤ 45 lbs vs. > 45 lbs

USA, midwifery practices

1,500

All weights/BMI

Fair

Total weight gain: Last prenatal assessment

Jain et al., 200777

Pregravid weight: Not stated

G1: WG ≤ 15 lbs

G2: WG 15-24 lbs

G3: WG 25-35 lbs

G4: WG ≥ 35 lbs

USA, birth certificate records and Pregnancy Risk Assessment Monitoring System

Total weight gain: Birth certificate

7,661

All weights/BMI

Fair

Johnson et al., 199270

Pregravid weight: Self report collected at first antepartal visit

G1: total weight gain < 16 lbs

G2: total weight gain 16-25 lbs

G3: total weight gain 26-35 lbs

G4: total weight gain > 35 lbs

USA, prenatal clinics

3,191

Total weight gain: Last prenatal visit

All weights/BMI

Fair

Joseph et al., 200372

Pregravid weight: Data taken from standardized forms and hospital medical records—no mention of self report

G1: < 5 kg

G2: 5-9 kg

G3: 10-14 kg

G4: 15-19 kg

G5: ≥ 20 kg

Nova Scotia Atlee Perinatal Database

100,259

All weights/BMI

Total weight gain: Not explained by authors—data taken from maternity records

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

Greater weight gain in pregnancy was not associated significantly with route of delivery

Prepregnancy BMI category, total prenatal weight gain category, induction of labor, newborn birthweight ≥ 4,000 g, gestational age > 41 weeks, and race/ethnicity

AOR for primiparous cesarean delivery (from model including interaction term for overweight/obese + > 25 lbs weight gain)

G1: 0.95 (0.59-1.52)

G2: 1.0 (ref)

G3: 1.10 (0.76-1.60)

G4: 1.62 (1.10-2.39)

AOR for multiparous cesarean delivery (from model including interaction term for overweight/obese + > 25 lbs weight gain)

G1: 1.11 (0.60-2.04)

G2: 1.0 (ref)

G3: 1.08 (0.63-1.85)

G4: 1.95 (1.02-3.72)

Maternal age, pregravid BMI, parity, education, race/ethnicity, US/foreign origin, interaction terms for pregravid BMI and weight gain

AOR for unscheduled cesarean (95% CI)

G1: 1.0

G2: 0.95 (0.6-1.5)

G3: 1.3 (0.86-1.95)

G4: 1.95 (1.32-2.87)

Prepregnancy weight quartile, height (tertile), BMI category, private physician (yes/no), maternal age, parity, birthweight, diabetes, hypertension, and maternal education

AOR for cesarean delivery (95% CI)

G1: 1.10 (1.00-1.20)

G2: 1.04 (0.99-1.10)

G3: 1.00

G4: 1.09 (1.05-1.14)

G5: 1.41 (1.35-1.47)

Age, parity, prepregnancy weight, smoking, pregnancy (singleton or multiple), hypertension, diabetes, previous fetal death, induction, epidural, physician type, time

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Kiel et al., 20074

Pregravid weight: Self report from data on birth certificate

All obese women

USA, birth registry

G1: Loss 10 lbs or more

G1: Loss 2-9 lbs

G1: No change

G1: Gain 2-9 lbs

G1: Gain 10-14 lbs

G1: Gain 15-25 lbs

G1: Gain 25-35 lbs

120,170

Total weight gain: Abstracted from medical chart

Obese women only

Fair

Murakami et al., 200552

Pregravid weight: Self report at first visit to clinic

G1: < 8.5 kg

G2: 8.5-12.5 kg

G3: > 12.5 kg

Japan, hospital

633

Total weight gain: Based on last clinically measured weight prior to delivery

All weights/BMI

Fair

Purfield and Morin, 199569

Pregravid weight: Self report as noted in medical chart

G1: prepregnant weight increased by 25% or less

G2: prepregnant weight increased by more than 25%

USA, Tertiary care medical center

104

Total weight gain: Weight at admission to hospital for birth

Normal weight women only

Fair

Rosenberg et al., 200571

Pregravid weight: Self report on birth certificate

< 41 vs. ≥ 41 pounds

USA, vital statistics data

329,988

Total weight gain: Weight data on birth file

All weights/no BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

Compared with women who gained 15-25 lbs during their pregnancies, those who gained less weight had significantly lower odds of preeclampsia, cesarean delivery, and LGA births, but higher odds for SGA births

Age, race, parity, education, poverty (enrollment in Medicaid, WIC, food stamp programs), tobacco use, chronic hypertension

Magnitude differed by obesity classification, even after adjusting for known or suspected confounders

AOR for cesarean delivery (95% CI)

G1: 1.08 (0.56-2.07)

G2: 1.00

G3: 1.23 (0.61-2.48)

Maternal age, parity, smoking, prepregnancy BMI, and gestational age (weeks)

Higher rate of vacuum extraction and cesarean delivery and lower rate of spontaneous vaginal delivery with excessive weight gain

Vacuum extraction

G1: n = 14

G2: n = 25

NA

low forceps

G1: n = 8

G2: n = 8

No difference in forceps delivery and vaginal delivery by weight gain status

Cesarean section

G1: n = 3

G2: n = 10

χ2 = 15.87, P = 0.001 for all 4 modes of delivery by weight groups

Vaginal delivery

G1: n = 27

G2: n = 9

AOR for primary cesarean (95% CI): 1.38 (1.34-1.41)

Age, parity, GDM, pregnancy-induced hypertension, preeclampsia, prepregnancy weight, chronic diabetes, chronic hypertension, marital status, maternal education, mother’s birthplace, prenatal care payer, social risk, trimester prenatal care began

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Shepard et al., 199875

Pregravid weight: Self report before 15 weeks of gestation

Proportional weight gain (total weight gain/prepregnancy weight) and absolute weight gain

USA, obstetrical practices

2,301

Total weight gain: Self report of weight at delivery

All weights/BMI

Fair

Sherrard et al., 200778

Pregravid weight: Self report

Rate of weight gain (kg/wk)

G1: Low (≤ 0.17)

G2: Normal (0.18-0.50)

G3: High (> 0.50)

Canada, hospital database

63,390

Total weight gain: Self report or measured

All BMIs

Fair

Witter et al., 199576

Pregravid weight: Self report, unclear at what timepoint

Pregnancy weight gain (kg)

USA,obstetric database at major medical center

4,346

Total weight gain: Weight recorded at last prenatal visit

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

G1: Proportional Gain: Adjusted Relative Risk (95% CI)

G2: Absolute Gain: Adjusted RR (95% CI)

Underweight (< 19.4), ≤ median

G1: 1.00

G2: 1.00

Low-Average (19.5-22.4), > median

G1: 2.35 (1.06-5.21)

G2: 1.62 (0.94-3.02)

Preeclampsia, gestational diabetes, placental problems, fetal distress, macrosomia, induction, maternal age and height, parity, ethnicity, and marital status

High-Average (22.5-28.4), ≤ median

G1: 2.78 (1.26-6.12)

G2: 1.80 (1.01-3.21)

Underweight (< 19.4), > median

G1: 2.08 (0.86-5.04)

G2: 1.20 (0.56-2.59)

High-Average (22.5-28.4), > median

G1: 3.06 (1.40-6.73)

G2: 2.02 (1.14-3.57)

Low-Average (19.5-22.4), ≤ median

G1: 1.62 (0.90-3.67)

G2: 1.00 (0.54-1.84)

Obese (> 28.5), ≤ median

G1: 3.25 (1.40-7.54)

G2: 2.13 (1.12-4.08)

Obese (> 28.5), > median

G1: 2.69 (1.18-6.16)

G2: 1.65 (0.90-3.03)

AOR for unlabored cesarean, primary

G1: 0.79 (0.59-1.05)

G2: 1.00 (ref)

G3: 1.03 (0.64-1.64)

AOR for unlabored cesarean, repeat

G1: 0.91 (0.76-1.09)

G2: 1.00 (ref)

G3: 1.38 (1.04-1.83)

BMI, gestational diabetes, pregnancy-induced hypertension, macrosomia, socioeconomic factors, parity, and maternal age

AOR for labored cesarean, primary

G1: 0.77 (0.68-0.86)

G2: 1.00 (ref)

G3: 1.40 (1.23-1.60)

AOR for labored cesarean, repeat

G1: 0.79 (0.54-1.15)

G2: 1.00 (ref)

G3: 1.22 (0.72-2.09)

AOR for cesarean (95% CI): 1.04 (1.02-1.05)

Age, pregravid BMI, height, at least one previous viable pregnancy, diagnosis of preeclampsia during the current pregnancy, previous cesarean delivery

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Bianco et al., 199854

Pregravid weight: Unclear

G1: 0 or weight loss

G2: 1-15 lbs

G3: 16-25 lbs

G4: 26-35 lbs

G5: > 35 lbs

USA, major medical center

11,926

Total weight gain: Weight from before 36 weeks gestation or not within 4 weeks of delivery

BMI OF 27 and 34 are excluded from analysis

Poor

Maternal weight gain outcomes by BMI presented for morbidly obese women only, N: 613

Brennand et al., 200549

Pregravid weight: Routine prenatal care medical records, measured within 14 weeks of gestation

Primigravid women (maternal weight gain outcomes by BMI presented only for obese women)

G1: Obese—low weight gain (< 7 kg)

G2: Obese—acceptable weight gain (7-11.5 kg)

G3: Obese—excessive weight gain (> 11.5 kg)

G4: Total

Canada, medical records

603

All weights/BMI

Total weight gain: Based on last clinically measured weight prior to delivery: within 4 weeks of birth

Poor

Primigravid women (maternal weight gain outcomes by BMI presented only for obese women)

Ekblad and Grenman, 199268

Pregravid weight: Data from records, unclear if self reported

G1: weight gain < 5 kg

G2: weight gain ≥ 20 kg

G3: reference (normal prepregnancy weight and normal weight gain [undefined])

Finland, hospital

357

Total weight gain: Routine prenatal care or maternity records based on last clinically measured weight prior to delivery

Normal weight only

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

Cesarean %

G1: 25.8%

G2: 26.8%

G3: 28.8%

G4: 35.0%

G5: 33.8% (P = NS)

 

NA

Cesarean section (%)

G1: 25.3

G2: 23.5

G3: 23.7

 

NA

χ2P = 0.952

G4: 24.1

 

Normal vaginal delivery (%)

G1: 90 P < 0.05 compared to reference category

G2: 64

G3: 71

Breech (%)

G1: 1

G2: 0

G3: 2

NA

Cesarean section—elective%

G1: 3

G2: 5

G3: 13

Forceps or vacuum delivery (%)

G1: 3

G2: 13

G3: 5

Cesarean section—emergency%

G1: 3

G2: 18

G3: 9

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Jensen et al., 200559

Pregravid weight: Records or self report of pregravid BMI

G1: GWG 5.0-9.9 kg

G2: GWG 10.0-14.9 kg

G3: GWG ≥ 15 kg

Denmark, university hospitals

481

Total weight gain: Last prenatal assessment

Obese only

Poor

Kabiru and Raynor, 200451

Pregravid weight: First prenatal visit

Primary cesarean

G1: normal BMI, no change in BMI between first prenatal visit and delivery

G2: normal BMI, 1 category increase in BMI between first prenatal visit and delivery

G3: normal BMI, > 1 category increase in BMI between first prenatal visit and delivery

G4: overweight BMI, no change in BMI between first prenatal visit and delivery

G5: overweight BMI, 1 category increase in BMI between first prenatal visit and delivery

G6: overweight BMI, > 1 category increase in BMI between first prenatal visit and delivery

USA, hospital

5,131

Total weight gain: Weight at admission for birth

All BM’s > 20I

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

OR for cesarean delivery (95% CI)

G1: 1.0

G2: 2.4 (1.1-5.3)

G3: 3.0 (1.4-6.4)

G4: 3.6 (1.6-7.8)

P for trend = 0.002

2-h OGTT result, maternal age, prepregnancy BMI, gestational age (continuous variables), parity, smoking, ethnic background, and clinical center (categorical variables

Operative vaginal delivery

G1: 11.4

G2: 12.4

G3: 12.2 P = 0.837

G4: 8.4

G5: 11.4

G6: 17.3 P < 0.001

Pregravid BMI, none other

Cesarean delivery rate for failure to progress

G1: 2.5

G2: 6.5

G3: 10.2 P = 0.203

G4: 3.5

G5: 6.9

G6: 10.2 P = 0.002

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Wataba et al., 200661

Pregravid weight: Unreported

Rate of weight gain, categorized differently across different BMI groups

Japan, academic medical center

Total weight gain: From hospital database/register

21,718

All weights/BMI

Poor

Young et al., 200274

Pregravid weight: Self reported

G1: < 30 lbs

G2: 30-35 lbs

G3: > 35 lbs

USA, private practice

3,375

Total weight gain: Based on last clinically measured weight prior to delivery

All weights/BMI

Poor

AOR, adjusted odds ratio; BMI, body mass index; G, group; GDM, gestational diabetes mellitus; kg, kilogram; lbs, pounds; LGA, large-for-gestational age; SGA, small-for-gestational age.

which did not control for route of previous delivery, did not find any association between gestational weight gain and route of delivery.67

Six studies defined gestational weight gain in categories that allowed for the identification of both low and high weight gain, across a spectrum of pregravid weight categories;52,58,70,72,74 of these, one was rated poor quality74 and the remainder fair. One study showed no difference in cesar-

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

 

Confounders and Effect Modifiers Included in Analysis

For nulliparous, low BMI women:

Higher risk of cesarean delivery for women with weight gain ≥ 0.4 kg/week (AOR: 2.30 [95% CI, 1.06-4.98] compared with women gaining 0.25-0.3 kg/week)

For nulliparous, high BMI women:

No increased risk

Parity, baseline BMI

For parous, medium BMI women:

Higher risk of cesarean delivery for women with weight gain 0.25-0.3 kg/week (AOR: 1.49 [95% CI, 1.09-2.04] compared with women gaining 0.20-0.25 kg/week)

For nulliparous, medium BMI women:

Higher risk of cesarean delivery for women with weight gain ≥ 0.4 kg/week (AOR: 1.61 [95% CI, 1.21-2.14] compared with women gaining 0.25-0.3 kg/week) and for women with weight gain 0.35-0.4 kg/week (AOR: 1.68 [95% CI, 1.22-2.30] compared with women gaining 0.25-0.3 kg/week)

No data presented on cesarean delivery for other BMI groups for parous women

Increase in overall cesarean delivery rate with increased weight gain was significant at all BMI levels

 

BMI

ean delivery by weight gain category.52 All others showed some patterns of association with higher levels of weight gain, although the magnitude of the effect varied.58,70,72,74 Three studies found similar thresholds for the rise in risk of cesarean delivery, namely, weight gains in excess of 15 kg72 or greater than 35 pounds.70,77 One study looked at both relatively low weight gain (< 8 kg) and relatively high weight gain (> 16 kg) in comparison with

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

weight gain of 8 to 16 kg.58 The study found no statistically significant risk of cesarean delivery for low or normal BMI categories but significantly higher risk with higher weight gain for overweight, obese, and morbidly obese women.58 One study examined the effects of pregravid weight, gestational weight gain, and the interaction between the two as predictors of cesarean delivery for primiparous and multiparous women (defined in two different ways). The study found that pregravid overweight or obese status as well as weight gain over 35 pounds are associated with the risk of cesarean delivery for primiparous women, but no significant effect of the interaction between weight gain and pregravid weight. The study did not find consistently significant effects of these variables on cesarean delivery for multiparous women; the previous route of delivery, a likely confounder, was not controlled in these analyses.

Results across BMI categories for rate of weight gain. Two studies, one rated fair78 and the other poor,61 examined the rate of weight gain across a range of pregravid weight categories. The fair study separately examined the risks of primary and repeat cesarean, with and without labor in models that accounted for gestational diabetes, pregnancy-induced hypertension, macrosomia, socioeconomic factors, parity, or maternal age. The study found that a high rate of weight gain (> 0.5 kg/week) significantly increased the risk of a labored primary cesarean, while a low rate of weight gain (≤ 0.17 kg/week) significantly reduced the risk, compared with an average rate of weight gain (0.18-0.50 kg/week). High rate of weight gain significantly increased the risk of unlabored repeat cesareans. The rate of weight gain during pregnancy did not predict the risk of primary unlabored cesarean or repeat labored cesarean. In contrast, pregravid overweight and obese status was a significant risk factor for all types of cesarean delivery. The poor study examined associations between cesarean delivery and rates of weekly weight gain (seven categories), categorized differently across different BMI groups (three groups) and parity (two categories), resulting in 42 comparisons.61 As with the fair study, a subset of results were significant, suggesting that for nulliparous women with low or medium BMI, high rates of weight gain increased the risks of cesarean delivery. Specifically, the study found:

  • among nulliparous, low-BMI women, a higher risk of elective cesarean delivery for women with weight gain ≥ 0.4 kg per week (AOR: 2.30 [1.06-4.98]) than for women gaining between 0.25 and 0.3 kg per week.

  • among nulliparous, medium-BMI women, a higher risk of elective cesarean delivery

    • for women with weight gain ≥ 0.4 kg per week (AOR: 1.61

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

[1.21-2.14]) than for women gaining 0.25 to 0.3 kg per week and

  • for women with weight gain of 0.35 to 0.4 kg per week (AOR: 1.68 [1.22-2.30]) than for women gaining 0.25-0.3 kg per week.

The study examined risk of emergency (rather than elective) cesarean for high BMI nulliparous women and failed to find an association with gestational weight gain rates.

In examining outcomes for parous women, with a single exception—a higher risk of cesarean delivery for women with weight gain 0.25-0.3 kg/wk (AOR, 1.49 [1.09-2.04]) than for women gaining 0.20 to 0.25 kg/week—the poor study did not find statistically significant effects for rate of weight gain on cesarean delivery for parous, medium-BMI women. No data were presented on cesarean delivery (emergency or elective) for low or high BMI groups for parous women.


Results across BMI categories for continuous measures of weight gain Of the 15 studies that considered a range of pregravid weight categories, two fair studies modeled gestational weight gain as a continuous variable.73,76 Both found significantly higher risks of cesarean delivery with increasing weight. One study identified the progression of AOR of cesarean delivery weight gain for every 5 pounds of gestational weight gain to be 1.094 (95% CI, 1.074-1.115).73 The second study calculated the attributable risk for cesarean delivery of gaining more than 16 kg to be 6.9 percent.76 Both studies account for route of previous delivery.


Results across BMI categories for other measures of weight gain Of these same 15 studies, three (1 fair,75 and 2 poor51,53,68) defined gestational weight gain as a function of pregravid weight.51,68,75 Two of three studies controlled for previous route of delivery by limiting their sample to primary cesareans. The fair study used underweight women who gained less than the median for proportional weight gain (total weight gain/prepregnancy weight) as the referent.75 This study found higher risks of cesarean delivery for all other categories, although risks were statistically significant only for women in the high and obese BMI category in all weight gain categories and women in the average BMI category who gained less than the median proportional weight gain. One poor-quality study characterized weight gain as change in BMI class between prepregnancy weight and at delivery. BMI categories were defined as follows: normal, BMI 20 to 24.9; overweight, BMI 25 to 29.9; obese I, BMI 30 to 34.9; obese II, BMI 35 to 39.9; morbid obesity, BMI ≥ 40.51 This study found no statistically significant association between weight gain and cesarean delivery among normal-BMI women but did find a positive association for high-BMI women. The extent to which

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

these results corroborate findings from the fair study is hard to determine given the differences in the reference category, but both studies imply that increased risks of cesarean are pronounced among overweight and obese women. A third study, also of poor quality, examined differences in route of delivery between women with normal prepregnancy weight and weight gain during pregnancy with those with abnormal weight gain (≥ 20 kg or ≤ 5 kg) during pregnancy; the study did not specify the prepregnancy weight status of women in these “abnormal” weight gain categories.68 Unlike the other two studies in this category, the rates for cesarean delivery were not statistically significantly different across groups. The study did find a statistically significant higher rate of normal vaginal delivery for low weight gain women compared with the reference category of normal prepregnancy weight and weight gain. Notably, this study did not control for route of previous delivery.

Results within BMI categories for other measures of weight gain. Two studies were limited to women of normal BMI.25,69 Both suggested an increase in the risk of cesarean delivery with increasing weight gain, defined in one study as 25 percent gain over prepregnancy weight,69 and in the other as a weight gain > 35 pounds as compared with a weight gain of 30 to 35 pounds. Weight gain of < 30 pounds was associated with a lower risk of cesarean delivery, suggesting a linear increase in the risk of cesarean delivery with weight gain for women of normal weight. One of the two studies controlled for previous cesarean delivery by limiting its sample to primigravidas.69

Four studies limited their analysis to obese women or morbidly obese women.4,49,54,59 Of these, two studies (both rated poor quality) suggested no difference in cesarean delivery outcomes by gestational weight gain.49,54 Neither accounted for route of previous delivery.

The other two studies suggested that the risk of cesarean delivery increased with higher levels of weight gain for obese and morbidly obese women.4,59 One poor study suggested that risk increases with higher levels of weight gain.59 Compared with the risk of cesarean delivery for women gaining < 5 kg, the results were as follows: AOR of cesarean delivery for women gaining 5 to 9.9 kg, 2.4 (95% CI, 1.1-5.3); AOR for women gaining 10 to 14.9 kg, 3.0 (95% CI, 1.4-6.4); and AOR for women gaining ≥ 15 kg, 3.6 (95% CI, 1.6-7.8).59 The other study suggested that women who had lower weight gain than women who gained 15 to 25 pounds had lower risks of cesarean delivery, but the magnitude of the association varied by obesity classification.4 Overall, across a range of outcomes the study suggested that minimal risk may correspond to a weight gain of 10 to 25 pounds for class I obese women (BMI 30-34.9), a weight gain of 0 to 9 pounds for class II obese women (BMI 35-39.9), and a weight loss of 0 to 9 pounds for class III obese women (BMI > 40). Neither of these studies controlled for route of previous delivery.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results for instrumental delivery Five studies examined instrumental delivery in addition to cesarean delivery.25,51,58,68,69 Two found no association.25,68 Of the remaining studies, one found a higher risk of instrumental delivery with increased weight gain only for normal BMI and overweight women,58 and a second found this only for overweight women.51 A third study, limited to women of normal weight, examined differences in the rate of vacuum extraction and forceps delivery by amount of weight gain; it found a higher rate of vacuum extraction with excessive weight gain but no difference in rate of forceps delivery.69


Results controlling for confounding Studies varied in their adjustment for confounding factors. Seven studies controlled for route of previous delivery by limiting their sample to primary cesarean51,71,72,75 or primigravidas.69,73,74 Three studies included multigravidas but accounted for previous cesarean delivery in the analysis.76-78 The remaining 11 studies did not control for route of previous delivery.4,25,49,52,54,58,59,61,67,68,70

Of the 10 studies that controlled for route of previous delivery, five studies examined underlying health risks (e.g., preeclampsia, pregnancy-induced hypertension) as predictors of cesarean delivery; all five found these health factors to be significantly associated with risks of cesarean delivery.71,72,75,76,78

Vaginal birth after cesarean

Study characteristics One U.S. cohort study (rated poor quality) examined the effect of weight gain on the success of vaginal birth after cesarean (VBAC) (Evidence Table 12).79


Overview of results A single poor study found that gestational weight gain of 40 pounds or more increased the risk of VBAC failure.


Results Women who gained more than 40 pounds during pregnancy were less likely to have VBAC success than women who gained 40 pounds or less (OR, 0.65; 95% CI, 0.42-0.98). This study controlled for previous normal spontaneous vaginal delivery, previous VBAC, diabetes, induction, birthweight > 4,000 g, recurrent indication, one layer closure, pregnancy complications, and BMI, but it failed to account for age or parity. The study suggested that pregravid BMI was also a predictor of VBAC success, with lower pregravid BMI being predictive of success.

Vaginal lacerations

Study characteristics Two cohort studies examined vaginal lacerations (Evidence Table 13).51,68 One U.S. study (rated poor quality) examined the incidence of third- or fourth-degree lacerations among women.51 Weight gain was characterized as change in BMI class between prepregnancy

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

weight and weight at delivery. BMI categories were defined as follows: normal, BMI 20 to 24.9; overweight, BMI 25 to 29.9; obese I, BMI 30 to 34.9; obese II, BMI 35 to 39.9; morbid obesity, BMI ≥ 40. The second study (described earlier, also rated poor quality) was set in Finland.68 It examined the rate of vaginal repairs for women with normal prepregnancy weight and weight gain during pregnancy and for those with abnormal weight gain (≥ 20 kg, or ≤ 5 kg) during pregnancy.68


Overview of results Two studies, both of poor quality, did not report consistent results on the effects of gestational weight gain on vaginal lacerations.


Results The U.S. study found no differences in the incidence of third-and fourth-degree lacerations among women who were overweight before pregnancy.51 It did find a statistically significant difference among normal weight women; the incidence of lacerations rose from 24 percent for women with no change in BMI category to 29.3 percent for women gaining enough to change weight status by one BMI category and to 31.7 percent for women who gained enough to change weight status by more than one BMI category. The Finnish study found no statistical differences between study and control mothers in the rate of repair of second- or third-degree lacerations.68 Neither study controlled for any variable other than pregravid BMI.

Shoulder dystocia

Study characteristics Three studies, set in Ireland,80 the United States,51 and Finland,68 examined the effect of gestational weight gain on shoulder dystocia (Table 9, Evidence Table 14). The Irish study, a case-control investigation (rated poor) comparing cesarean delivery for shoulder dystocia with cephalic vaginal term deliveries, distinguished between two groups of gestational weight gain (< 12 kg and ≥ 12 kg).80 The Finnish study (described earlier and rated poor quality), stratified its sample by weight gain categories, comparing women with normal prepregnancy weight and weight gain during pregnancy with those with abnormal weight gain (≥ 20 kg or ≤ 5 kg) during pregnancy.68 The U.S. case-control study (also rated poor quality), stratified its sample between normal and overweight BMI categories and examined the effect of change in BMI class between prepregnancy weight and weight at delivery. The Irish study defined shoulder dystocia to include mild, moderate, and severe cases;80 the other two studies did not define their outcome variable.51,68


Overview of results Only one80 of three poor studies found a positive association between gestational weight gain and shoulder dystocia.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 9. Gestational Weight Gain and Shoulder Dystocia

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Ekblad and Grenman, 199268

Pregravid weight: Data from records, unclear if self reported

G1: weight gain ≤ 5 kg

G2: weight gain ≥ 20 kg

G3: reference (normal prepregnancy weight and normal weight gain [undefined])

Shoulder dystocia%

G1: 3

G2: 2

G3: 0.6

NA

Finland, hospital

Total weight gain: Last clinically measured weight prior to delivery

357

Normal weight only

Poor

Geary et al., 199580

Pregravid weight: First prenatal visit

Weight gain < 12 kg and ≥ 12 kg for cases shoulder dystocia and controls

Maternal weight gain < 12 kg

Parity

Previous birth ≥ 4,000 g

Ireland, hospital

Total weight gain: Not described

G1: Cases with shoulder dystocia

G2: Controls

G1: 59.1%

G2: 74.1%

OR 2.0 (1.6-2.2)

363

All weights/BMI

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Kabiru and Raynor, 200451

Pregravid weight: First prenatal visit

G1: normal BMI, no change in BMI between first prenatal visit and delivery

G2: normal BMI, 1 category increase in BMI between first prenatal visit and delivery

G3: normal BMI, > 1 category increase in BMI between first prenatal visit and delivery

G4: overweight BMI, no change in BMI between first prenatal visit and delivery

G5: overweight BMI, 1 category increase in BMI between first prenatal visit and delivery

G6: overweight BMI, > 1 category increase in BMI between first prenatal visit and delivery

Shoulder dystocia%

G1: 0.5

G2: 1.4

G3: 1.1

P = 0.278 for associations within normal BMI categories

NA

USA, hospital

Total weight gain: Weight at admission for birth

5,131

All weights/BMI

Poor

G4: 1.0

G5: 1.8

G6: 1.9

P = 0.357 for associations within overweight BMI categories

BMI, body mass index; g, gram; G, group; kg, kilogram; N, number; OR, odds ratio.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results The three studies found rates of shoulder dystocia ranging from 0.6 percent to 1.4 percent.51,68,80 Two studies reported no statistically significant differences in rates of shoulder dystocia between weight gain groups.51,68 The Irish case-control investigation found that higher gestational weight gain during pregnancy was a significant predictor of shoulder dystocia (OR, 2.0; 95% CI, 1.6-2.2; P = 0.015). The authors calculated positive predictive value percentages from the study group and applied them to the total hospital population of singleton vaginal deliveries without shoulder dystocia over the same time period. These results suggest a positive predictive value of 1 percent for shoulder dystocia when gestational weight gain is 12 kg or greater.

The Irish study accounted for a subset of confounders and effect modifiers other than pregravid BMI.80 Multiparity and birth of a previous heavy baby were significant and independent determinants for shoulder dystocia, in addition to gestational weight gain. However, the investigators noted that each predictor individually accounted for less than 2 percent of the positive predictive value for shoulder dystocia, and all three put together accounted for less than 3 percent.

Cephalopelvic disproportion

Study characteristics Two U.S. cohort studies examined the association between gestational weight gain and cephalopelvic disproportion (CPD) (Evidence Table 15).25,74 One study, using Missouri birth certificate data, defined CPD as the condition when the size, presentation, or position of the fetal head to the maternal pelvis prevented cervical dilation or descent of the fetal head.25 This study controlled for a range of demographic confounders but not for maternal health characteristics.25 The other study (rated poor quality) defined CPD among primiparous women as little or no progress over a 2- to 4-hour period, with contractions documented to be adequate and cervix dilated to at least 3 cm or preferably 4 cm. However, if the delivering physician defined the indication as CPD, the decision was accepted without chart review, despite the definitions listed earlier.74

Both studies defined weight gain in categories: < 30 pounds, 30 to 35 pounds, and > 35 pounds. The study using birth certificate data limited inclusion to normal weight women (pregravid BMI 19.8-26.0);25 the other study examined the association between gestational weight gain and CPD across four pregravid BMI categories: < 20, 20 to 25, 25 to 30, and > 30.


Overview of results Both studies (1 fair25 and 1 poor74) showed that, for normal-weight women, the risk of CPD rose with higher gestational weight gain


Results The fair study reported an AOR of 1.58 (95% CI, 1.44-1.75) for women gaining > 35 pounds compared with women gaining 25

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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to 30 pounds, after adjusting for maternal age, maternal race or ethnicity, maternal education, Medicaid status, tobacco use, alcohol use, maternal height, prior pregnancy, adequacy of prenatal care, child’s sex, and child’s birth year.25 The poor study showed similar results, with an unadjusted OR of CPD of 1.85 (95% CI, 1.63-2.06) for normal-weight women gaining > 35 pounds compared with women gaining < 30 pounds. This study also showed an increased risk of CPD for underweight women gaining > 35 pounds compared with women gaining < 30 pounds (unadjusted OR: 3.8; 95% CI, 3-4.6). The relationship between weight gain and CPD was not statistically significant at higher pregravid BMI levels.74

Complications of labor and delivery

Study characteristics Two retrospective cohort studies, one from Iceland53 and the other from the United States,81 evaluated the impact of gestational weight gain on complications of labor and delivery (Evidence Table 16).


Overview of results Two studies, of fair53 and poor81 quality respectively found conflicting evidence on the risks of complications. One failed to find statistically significant results;53 the other reported that gestational weight gain of more than 40 pounds increased the risk for the previously listed complications by 40 percent.81


Results The fair study from Iceland analyzed the quartiles of total weight gain in women with normal pregravid BMIs (19.5-25.5) to determine the impact of weight gain on labor and delivery processes.53 After adjusting for age, height, parity, gestational length, and birthweight, they found that weight gain of 11.5 to 16.0 kg was associated with the highest likelihood of a normal vaginal delivery, defined to include no shoulder dystocia and no asphyxia, and the least likelihood of operative procedures including cesarean delivery and forceps- or vacuum-assisted deliveries. The findings of this study, however, were not statistically significant.

The poor U.S. study enrolled 493 women at 37 or more weeks of gestational age to determine the relationship between various lifestyle choices and complications in term pregnancy.81 Complications included dystocia, postpartum hemorrhage, retained placenta, fetal and neonatal distress, and pregnancy-induced hypertension. All complications were grouped together for the analysis. Smoking had a protective effect against complications, but entering pregnancy with excess weight for height and gaining more than 40 pounds during gestation both predicted complications. A gestational weight gain of more than 40 pounds increased the risk for the previously listed complications by 40 percent.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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Birth Outcomes
Preterm birth

Study characteristics Twelve studies (Table 10, Evidence Table 17) examined the relationship between weight gain and birth outcomes.23,59,65,71,82-89 These include eight cohort studies,59,65,82-86,89 two case-control studies,87,88 and two cross-sectional studies.23,71 The majority of the studies defined preterm birth as delivery occurring prior to 37 weeks of gestation; the one exception defined it as delivery between 24 and 35 weeks of gestation.87 Each study defined weight gain differently. Two studies examined associations of weight gain with early and late preterm birth,23,65 and two studies examined associations across subtypes of preterm delivery.65,84


Overview of results Taken collectively, the results of these two good,84,88 seven fair,23,65,71,82,85,86,89 and three poor53,59,83,87 studies suggest an association between preterm birth and both low and high rates of weight gain and with low total weight gain, with one study reporting a 16 percent decrease in preterm birth associated with a 1 kg increase in maternal weight. The cut points for low and high weight gains and the severity of the risks of preterm birth associated with them differ by pregravid BMI. In general, low rates of weight gain were ≤ 0.37 kg per week and high rates of gain were > 0.52 kg per week throughout gestation, with the greatest risks found among underweight women. However, as pregravid BMI increases, the risk of preterm birth decreases for women gaining in the lower range of the low rate of weight gain and increases for women gaining in the lower range of the high rate of weight gain, such that the range of adequate rates of weight gain is shifted down for heavier women compared to their lighter counterparts. Some evidence also suggests that low rate of weight gain is associated with greater risks of early preterm birth as well as preterm birth due to premature rupture of the amniotic membranes.

Detailed results from categorical measures of total rate of weight gain. Four studies used categorical definitions of rate of weight gain averaged for the entire length of gestation;85,86,88,89 one study was rated good88 and the others rated fair.85,86,89 In the good study,88 a rate of weight gain of < 0.27 kg per week was not associated with preterm birth (OR, 1.56; 95% CI, 0.94-2.58). Among the fair studies, all three studies found evidence of an association between low rate of weight gain and preterm birth, and two studies found evidence of an association between high rate of weight gain and preterm birth.86,89

One study used a retrospective, U.S.-hospital-based cohort of deliveries from 1976 to 2001 to examine the association of preterm birth and gestational weight gain by maternal race or ethnicity.85 Weight gain was categorized into three groups based on rate of weight gain: < 0.27 kg per week,

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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TABLE 10. Gestational Weight Gain and Preterm Birth

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Kramer et al., 199588

Pregravid weight: Self-report

Gestational weight gain categories (kg/wk):

G1: < 0.27

G2: ≥ 0.27

Canada, University Hospitals

Total weight gain: Self-report

396

All weight/BMI

Good

Siega-Riz et al., 199684

Pregravid weight: Self-reported

Categories of 3rd trimester weekly weight gain rates (kg/week):

USA, Public Health Clinics (California)

Total weight gain: Measured

7,589

G1: Inadequate (Underweight, < 0.34; Normal weight, < 0.35; Overweight/Obese, < 0.30)

All weight/BMI

Good

G2: Adequate (Underweight, > 0.34; Normal, > 0.35; Overweight/Obese, > 0.30)

Carmichael et al., 199782

Pregravid weight: Self-report

Total gestational weight gain (continuous)

USA, University Hospital (California)

Total weight gain: Maternity Records

7,259

Nonobese

Fair

Dietz et al., 200623

Pregravid weight: Self-report

Categories of mean rate of gestational weight gain (kg/wk) during second and third trimesters stratified by pregravid BMI and type of preterm birth (very preterm, 20-31 weeks; moderate preterm, 32-36 weeks):

G1: < 0.12

G2: 0.12-0.22

G3: 0.23-0.68

G4: 0.69-0.79

G5: > 0.79

USA, Pregnancy Risk Assessment Monitoring System

Total weight gain: Birth Certificates

113,019

All weight/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

AOR (95% CI) for cases with preterm delivery versus controls

Parity, marital status, language, age, education, matched on smoking history

G1: 1.56 (0.94-2.58)

G2: 1.00 (reference)

AOR (95% CI) for rate of preterm birth:

G1: 1.91 (1.40-2.61)

G2: 1.00 (reference)

Iron status, parity combined with maternal age, ethnicity, hypertension (chronic or pregnancy induced), smoking status, week prenatal care began

AOR (95% CI) for rate of preterm labor:

G1:1.75 (1.15-2.64)

G2: 1.00 (reference)

AOR (95% CI) for rate of PPROM:

G1: 2.70 (1.35-5.42)

G2: 1.00 (reference)

Linear regression analysis of gestational age (days) as dependent variable and gestational weight gain (kg) as independent variable: Regression coefficient = 0.51; t-statistic = 13.1; P < 0.001

BMI, maternal age, infant sex cigarettes per day maternal height, parity, race, pattern of gain derived from quadratic curves

AOR (95% CI) of spontaneous preterm birth/kg increase in total weight gain: 0.84 (0.82-0.87)

In general, in comparison to women with normal BMI in G3: underweight women in G1-G5 and normal weight women in G1, G2, and G5 were at increased risk of very preterm births (AOR: 1.5-9.8). Underweight women in G1-G3 and G5 and normal women in G1, G2, and G5 were at increased risk moderate preterm births (AOR: 1.4-3.1). Overweight and obese women in G1 and G5 were at increased risk of very preterm birth (AOR: 2.3-2.5) but had no elevated risk of moderate preterm birth. Very obese women with G1, G4, G5 had increased risks of very preterm births (AOR: 2.1-2.8) and with G4 had increased risks of moderate preterm birth (AOR: 1.3)

Race, Medicaid recipient, parity, marital status

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Nohr et al., 200765

Pregravid weight: Self-reported

Rate of gestational weight gain (g/wk) for women with early preterm birth (22-33 weeks) with PPROM :

G1: < 275

G2: 276-675

G3: ≥ 676

Danish National Birth Cohort

Total weight gain: Self-reported

16,167

All weight/BMI

Fair

Rate of gestational weight gain (g/wk) for women with early preterm birth (22-33 weeks) without PPROM :

G4: < 275

G5: 276-675

G6: ≥ 676

Rate of gestational weight gain (g/wk) for women with late preterm birth (34-36 weeks) with PPROM:

G7: < 275

G8: 276-675

G9: ≥ 676

Rate of gestational weight gain (g/wk) for women with late preterm birth (34-36 weeks) without PPROM:

G10: < 275

G11: 276-675

G12: ≥ 676

Rosenberg et al., 200571

Pregravid weight: Self-report

Categories of total gestational weight gain (lbs):

USA, New York City birth files

Total weight gain: Self-report

G1: < 41

G2: ≥ 41

329,988

All weight/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

HR (95% CI):

G1: 2.1 (1.5-3.0)

G2: 1.0 (ref)

G3: 1.2 (0.8-1.8)

Pregravid BMI, age, height, parity, socio-occupational status, smoking alcohol consumption

HR (95% CI):

G4: 1.9 (1.3-2.6)

G5: 1.0 (ref)

G6: 1.9 (1.3-2.6)

HR (95% CI):

G7: 1.3 (1.0-1.6)

G8: 1.0 (ref)

G9: 1.2 (1.0-1.5)

HR (95% CI):

G10: 1.0(0.9-1.2)

G11: 1.0(ref)

G12: 1.0 (0.9-1.2)

AOR (95% CI) for Preterm Birth:

G1: 1.00 (reference)

G2: 0.54 (0.52-0.57)

Pregravid weight, chronic diabetes, GDM, chronic hypertension, PIH preeclampsia, maternal age marital status maternal education maternal birthplace, prenatal care payer, social risk, parity, trimester that prenatal care began

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Schieve et al., 199986

Pregravid weight: Self-reported

Rate of weight gain (kg/week) in percentiles stratified by Low, Average, High, and Obese pregravid BMI:

G1: 5th,0.10

G2: 10th, 0.16

G3: 25th,0.26

G4: 50th,0.35

G5: 75th, 0.46

G6: 90th, 0.57

G7: 95th, 0.65

USA, Pregnancy Nutrition Surveillance System (PNSS)

Total weight gain: Self-reported

266,172

All weight/BMI

Fair

Stotland et al., 200685

Pregravid weight: Medical Charts

Categories of rate of gestational weight gain (kg/wk):

USA, University Hospital (California)

Total weight gain: Medical Charts

15,101

G1: < 0.27

G2: 0.27 to 0.52

G3: > 0.52

Underweight/Normal BMI

Fair

Wen et al., 199089

Pregravid weight: Measured at first prenatal visit

Rate of weight gain (kg/wk) after 20 weeks gestation

USA, University Hospital (Alabama)

G1: < 0.24

G2: 0.24-0.57

G3: 0.58-0.74

G4: ≥ 0.75

17,149

Total weight gain: Medical records

All weight/BMI

Fair

Jensen et al., 200559

Pregravid weight: Self-report

Total gestational weight gain categories (kg):

Denmark, University hospital centers

Total weight gain: Hospital records

G1: < 5.0

G2: 5.0-9.9

G3: 10.0-14.9

G4: > 15.0

481

Obese

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

Reference category of rate of weight gain: 0.35-< 0.46 kg/wk RD of preterm birth varied by prepregnant BMI and gestational weight gain. Overall, women gaining 0.26-0.46 kg/wk had the lowest RD of preterm birth. The highest RD occurred for women gaining the least and most amount of weight, irrespective of prepregnant BMI; however, the highest RD of preterm births were among women of low BMI

None

AOR (95% CI) for preterm delivery < 37 weeks:

G1: 2.6 (2.1-3.2)

G2: 1.0 (reference)

G3: 1.0 (0.8-1.2)

Race, age pregravid BMI, year of delivery, parity, previous preterm birth, number of days between last weighing and delivery, smoking

AOR (95% CI) for preterm delivery < 34 weeks:

G1: 3.0 (2.0-4.8)

G2: 1.0 (ref)

AOR for preterm birth:

G1: 1.52 (P < 0.05)

G2: 1.11 (NS)

G3: 1.00 (ref)

G4: 1.71 (P < 0.05)

Race, parity, infant sex, marital status, education, age, previous preterm delivery, smoking, alcohol consumption, drug use, height, pregravid weight

Percent (%) preterm delivery by weight gain categories:

NA

G1: 6.5

G2: 6.0

G3: 4.6

G4: 2.5

P for trend = 0.11

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured) Total Weight Gain (How Measured)

Definition of Groups

Spinillo et al., 199887

Pregravid weight: Self-report

G1: Prepregnancy BMI ≤ 19.5 and 2nd/3rd trimester weight gain ≤ 0.37 kg/wk

Italy, University Hospital

Total weight gain: Medical records

690

G2: Prepregnancy BMI > 19.5 and 2nd/3rd trimester weight gain ≥ 0.37 kg/wk

All weight/BMI

Poor

G3: Prepregnancy BMI ≤ 48 kg and 2nd/3rd trimester weight gain ≤ 0.37 kg/wk

G4: Prepregnancy BMI > 48 kg and 2nd/3rd trimester weight gain ≤ 0.37 kg/wk

Velonakis et al., 199783

Pregravid weight: Self-reported

Total gestational weight gain (continuous)

France, Hospital

Total weight gain: Measured

2040

All weight/BMI

Poor

AOR, adjusted odds ratio; BMI, body mass index; CI, confidence interval; HR, hazards ratio; kg, kilogram; n, number; OR, odds ratio; PPROM, preterm premature rupture of amniotic membranes; RD, risk difference; USA, United States of America; wk, week.

0.27-0.52 kg per week, and > 0.52 kg per week. Within the entire cohort and across four racial or ethnic groups (white, black, Latina, and Asian), the highest percentages of preterm birth occurred among women gaining < 0.27 kg per week. The adjusted odds of spontaneous preterm birth were 2.5 times higher in women with rates of weight gain < 0.27 kg per week than in women gaining 0.27 to 0.52 kg per week. The adjusted odds ratios for this association were statistically significant across the different racial or ethnic groups, ranging from 2.1 (95% CI, 1.4-3.1) for white women to 3.6 (95% CI, 2.2-6.0) for black women. No association between spontaneous preterm birth and rate of weight gain > 0.52 kg per week (relative to a weight gain of 0.27 to 0.52 kg per week) was seen either within the entire cohort or across the racial or ethnic groups.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

AOR (95% CI) for cases with spontaneous preterm delivery versus controls:

Pregravid BMI, pregravid weight, height, age, parity, smoking, social class education, infant sex

G1: 5.63 (2.35-13.8)

G2: 2.45 (1.60-3.75)

P = 0.06 for interaction between G1 and G2

G3: 5.29 (1.45-20.90)

G4: 2.42 (1.65-3.55)

P = 0.21 for interaction between G3 and G4

Regression analysis with gestational age (weeks) as the dependent variable and net gestational weight gain as the independent variable:

B = 0.191 (SE, 0.06)

P = 0.001

Age, race, gravidity, previous diseases, parity, abortions, marital status, pathology of index pregnancy, infant sex, height pregravid weight, job classification, alcohol, smoking, APGAR score, duration of pregnancy

Another study, conducted in a population of young, primarily black, disadvantaged women, found statistically significant higher odds of preterm delivery among women gaining < 0.24 kg per week and > 0.74 kg per week than among women gaining 0.58 to 0.74 kg per week.89

The final study used data collected from women participating in U.S. federally funded prenatal public health programs via the Pregnancy Nutrition Surveillance System (PNSS).86 Gestational weight gain was defined as rates of weight gain and net weight gain (kg/week) and categorized by the percentile distributions based on the total sample. Women with rates of weight gain between 0.35 and 0.46 kg per wk (the 50th through the 74th percentiles) were used as the reference for risk difference calculations. In general, the risk of preterm birth was highest among women with the small-

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

est and greatest rates of weight gain, < 0.10 kg per week and ≥ 0.65 kg per week, respectively. The lowest risks of preterm delivery occurred among women gaining between 0.26 and 0.46 kg per week (the 25th through the 74th percentiles). Preterm risk differences did vary by maternal pregravid BMI status. An increased risk of preterm birth was associated with rates of weight gain for the following pregravid BMI categories:

  • pregravid BMI < 19.8: < 0.26 kg per week;

  • pregravid BMI of 19.8 to 26.0: < 0.26 kg per week and > 0.65 kg per week;

  • pregravid BMI of 26.1 to 29.0: < 0.10 kg per week and > 0.65 kg per week; and

  • pregravid BMI > 29.0: ≥ 0.57 kg per week.

The results were similar when rates of weight gain per week excluded the first 14 weeks of gestation.


Results from categorical measures of trimester rate of weight gain Four studies used categorical definitions of rate of gestational weight gain measured during specific trimesters of pregnancy.23,65,84,87 All of the studies found evidence for an association between preterm birth and low rate of weight gain and two studies found evidence for an association between preterm birth and high rate of weight gain.


One study of good quality used a cohort of mainly Hispanic women recruited from public health clinics to examine the association between preterm birth and rate of weight gain during the third trimester.84 Women with preterm deliveries had significantly lower rates of third trimester weight gain than women with term deliveries, 0.50 (standard error of mean [SEM]: 0.02) kg per week versus 0.53 (SEM: 0.004) kg per week, respectively (P < 0.05). The odds of preterm birth were 1.91 (95% CI, 1.40-2.61) times greater among women with inadequate third trimester weight gains (defined as a rate of weight gain less than the 25th percentile of gain in each pregravid weight status: 0.34 kg/week, underweight; 0.35 kg/week, normal weight; 0.30 kg/week, overweight and obese) than among women with adequate rates of weight gain. When data were stratified by the type of preterm delivery, women with inadequate weight gains were 1.75 (95% CI, 1.15-2.64) times more likely to have preterm delivery resulting from preterm labor and 2.70 (95% CI, 1.32-5.42) times more likely to have preterm delivery resulting from preterm premature rupture of the amniotic membranes (PPROM) than women with adequate rates of weight gain.

One study, rated fair quality, used data from the Danish National Birth Cohort to assess the impact of gestational weight gain on early (22-

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

33 weeks), late (34-36 weeks), and all (22-36 weeks) preterm births with PPROM, without PPROM, and with medical inducement.65 Gestational weight gain was categorized as low (< 275 g/week), medium (275-675 g/week), and high (> 675 g/week) based on two self-reported measurements recorded at least 6 weeks apart between 12 and 37 weeks of gestation. Women with medium rates of weight gain were used as the reference. Overall, low rates of weight gain were significantly associated with an increased risk of early spontaneous preterm birth with and without PPROM and with all spontaneous preterm births with PPROM, adjusted odds ratios ranged from 1.5 to 2.1. High rates of weight gain were significantly associated with an increased risk of early spontaneous preterm births without PPROM (AOR, 1.9; 95% CI, 1.3-2.6) and early, late, and all medically induced early preterm births. However, when women with obesity-related diseases and abruptio placenta were excluded, the associations for medically induced preterm births were no longer significant.

Another fair quality study used information collected for the Pregnancy Risk Assessment Monitoring System (PRAMS) to examine the effect of rate of weight gain during the second and third trimesters on preterm birth.23 These investigators stratified women by prepregnancy BMI status and examined the risk of preterm birth in two categories: moderate length of gestation (32-36 weeks) and very short length of gestation (20 to 31 weeks). Second and third trimester rate of weight gain was categorized, in kg per week, as follows: < 0.12, 0.12-0.22, 0.23-0.68, 0.69-0.79, and > 0.79; the investigators also used five pregravid BMI groups: underweight (< 19.8), normal weight (19.8-26.0), overweight (26.1-28.9), obese (29.0-34.9), and very obese (≥ 35.0). Women of normal weight with rates of weight gain of 0.23 to 0.68 kg per week were used as the reference for analyses. After adjusting for covariates and excluding women with diabetes, hypertension, or small-for-gestational-age (SGA) infants, significant associations (AOR range, 1.3-3.1) were reported between moderate preterm birth and rates of weight gain as follows: < 0.69 and > 0.79 kg per week among underweight women; < 0.23 and > 0.79 kg per week among normal weight women; and 0.69 to 0.79 kg per week among obese and very obese women. Significant associations (AOR range, 1.5-9.8) were reported between very preterm birth and rates of weight gain as follows: all weight gain categories among underweight women; < 0.23 and > 0.79 kg per week among normal weight women; < 0.12 and > 0.79 kg per week among overweight and obese women; and < 0.12 and > 0.68 kg per week among very obese women. In general, the greatest odds were found among underweight women and in the extreme weight gain categories.

Results from a poor study87 were consistent with those of the other studies and revealed an overall increased odds of preterm birth (between 24

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

and 35 weeks’ gestation) with gestational weight gain ≤ 0.37 kg per week in the second and third trimesters; however, the odds were greater among women with pregravid BMI ≤ 19.5 compared to those with BMI > 19.5.


Results from categorical measures of total weight gain Two studies,59,71 one rated fair and the other poor, used categories of total weight gain. In the fair study, data from the New York City birth file from 1999 through 2001 was used to examine the odds of preterm birth associated with different levels of gestational weight gain.71 After adjusting for covariates, the investigators determined that the odds of preterm birth were significantly decreased (OR, 0.54; 95% CI, 0.52-0.57) among women who gained at least 41 pounds compared with women who gained less than 41 pounds. Results from the poor study,59 which used a population of obese women, showed the highest proportion of preterm birth among those with the lowest gestational weight gain (< 5.0 kg).


Results from continuous measures of weight gain The remaining two studies, one rated fair and the other poor, used gestational weight gain as a continuous measure.82,83 Both studies reported a significant increase in length of gestation for a 1 kg increase in total gestational weight gain.

In the fair study,82 simple regression techniques were used to develop a variable for pattern of weight gain that reflected the variation between a woman’s pattern of weight gain and a linear pattern of weight gain.82 Deviations in the pattern of weight gain, such as pronounced speeding up or slowing down of weight gain later in gestation, from an average pattern of weight gain were associated with decreased gestational age and increased risk of spontaneous preterm birth. A 1-kg increase in total gestational weight gain was associated with 0.51 day’s increase in gestational age (P < 0.001). The odds of spontaneous preterm birth were decreased by 16 percent for each 1-kg increase in total gestational weight gain (OR, 0.84; 95% CI, 0.82-0.87; P < 0.001).

Birthweight

Study characteristics Twenty-five studies examined the association between gestational weight gain and infant birthweight (Evidence Table 18).48,54,55,59,68,70,75,83,90-106 These studies consisted of various groups of women, in many different countries. Nine studies were completed outside the United States, in Canada,105 France,83,92 Italy,91,100 Denmark,59 Norway and Sweden,99 Finland,68 and Austria.93

One study observed the association for adolescent mothers.95 The association was also evaluated for mothers with gestational diabetes mellitus (GDM),100 mothers who had a positive diabetic screen but normal glucose tolerance levels,91 and obese glucose-tolerant women.59 Seven-

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

teen studies adjusted their analyses for multiple confounders, including maternal age, BMI, smoking, glucose levels, race, marital status, and parity.48,55,59,70,75,90-93,97-103,105


Overview of results The results for four good,48,98,103,10612 fair,55,65,70,75,92,93,97,99-102,104,105 and nine poor54,59,68,83,90,91,94-96 studies consistently demonstrate an association between higher gestational weight gain and birthweight.

Results from categorical measures of weight gain. Eight studies analyzed the relationship between weight gain and birthweight by categorizing gestational weight gain (Table 11).54,59,68,94,95,99,101,106 One study was rated to be of good quality,106 two of fair quality,99,101 and five of poor quality.54,59,68,94,95 These studies suggest a positive association between gestational weight gain and infant birthweight.

A U.S. study rated of good quality found that higher values for maternal weight near term, categorized by the percentage of standard weight-for-height, were associated with higher birthweight for black and Hispanic mothers.106 Specifically, black mothers > 135 percent of standard weight for height gave birth to infants that weighed on average 512 g more than infants born to black mothers < 100 percent of standard weight for height. Hispanic mothers > 135 percent of standard weight for height gave birth to infants that weighed on average 338 g more than infants born to Hispanic mothers < 100 percent of standard weight for height.

In one Scandinavian study (fair quality), estimated birthweights decreased by 131 g for women who gained less than 11 kg and increased by 164 g for women who gained more than 17 kg, as compared with estimated birthweights for women gaining between 11 and 17 kg.99 A fair-quality U.S. study examined patterns of weight gain and infant birthweight in a population of white nonobese women.101 Low weight gain by trimester was defined as having weight gain less than the 25th percentile. Infants of mothers with low weight gain in all three trimesters had weighed 248.1 g less, on average, than infants of mothers in other groups. Low weight gain for the first trimester was associated with a decrease in birthweight of 133 g; low weight gain for the second and third trimesters was associated with an 88.5 g decrease in birthweight.

The five poor-quality studies also found that increases in gestational weight gain resulted in larger infant birthweights.54,59,68,94,95 This trend held among studies of obese glucose-tolerant women,59 Finnish women,68 and adolescent mothers.94,95 One study stratified by maternal BMI and found that among women with low BMI (< 25) those that gained > 35 lbs had infants that were, on average, 273 g heavier than infants born to women gaining < 35 lbs. Among women with high BMI (> 25), women that gained > 35 lbs had infants that were, on average, 209 g heavier than infants

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 11. Total Gestational Weight Gain (categorical) and Infant Birthweight

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Hickey et al., 1990106

Pregravid weight: Self-report

Infant BW for groups defined by maternal weight near term (% of standard weight-for-height)

G1: 3,325 g ± 460

G2: 3,543 g ± 410

G3: 3,200 g ± 389

G4: 3,381 g ± 385

G5: 3,157 g ± 373

G6: 3,282 g ± 400

G7: 3,025 g ± 494

G8: 3,154 g ± 375

G9: 2,813 g ± 289

G10: 3,205 g ± 472

N/A

United States, prenatal clinics

Total weight gain: Routine prenatal care or maternity records

325

G1: > 135%, Black

G2: > 135%, Hispanic

G3: 120-135%, Black

G4: 120-135%, Hispanic

G5: 110-119%, Black

G6: 110-119%, Hispanic

G7: 100-109%, Black

G8: 100-109%, Hispanic

G9: < 100%, Black

G10: < 100%, Hispanic

All weight/BMI

Good

Abrams et al., 1995101

Pregravid weight: Self-report

G1: Infant BW among nonobese women

3,485.8 g ± 523.1

Maternal age, parity, pregravid BMI, height, smoking, infant sex, difference in weeks between the last measured weight and delivery

USA, university hospital

Total weight gain: Routine prenatal care or maternity records

4,420

Nonobese

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Zaren et al., 199799

Pregravid weight: Self-report

β is estimated change in infant BW (g)

G1: β = −131 (P = 0.0001)

G2: β = 164 (P = 0.0001)

Maternal age, height, pregravid weight, smoking

Norway and Sweden, university hospitals

Total weight gain: Routine prenatal care or maternity records

G1: GWG ≤ 11 kg:

G2: GWG ≥ 17 kg:

1,099

All weights/BMI

Fair

Bianco et al., 199854

Pregravid weight: Self-report

Infant BW for GWG:

G1: 3,302

G2: 3,192

G3: 3,337

G4: 3,506

G5: 3,453

(P < 0.05)

N/A

USA, medical center

G1: Weight loss or 0 lbs

G2: 1-15 lbs

G3: 16-25 lbs

G4: 26-35 lbs

G5: > 35 lbs

Total weight gain: Routine prenatal care or maternity records

613

Morbidly obese (BMI > 35)

Poor

Cherry et al., 199395

Pregravid weight: Measured by study investigators

Infant BW by Quartiles of weight gain

G1: 2,829 g

G2: 2,990 g

G3: 3,112 g

G4: 3,189 g

N/A

USA, hospital

RCT

Quartiles defined as weekly weight gain in g per cm height

Total weight gain: Routine prenatal care or maternity records

599

All weights/BMI

G1: Quartile 1 (≤ 1.87g)

G2: Quartile 2 (1.88-2.68g)

G3: Quartile 3 (2.69-3.58g)

G4: Quartile 4 (≥ 3.59g)

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Ekblad and Grenman, 199268

Pregravid weight: Medical records

Infant BW by group

G1: 3,538 g ± 535

G2: 3,284 g ± 880

G3: 3,803 g ± 538

N/A

G1: Normal prepregnancy weight and normal weight gain

G2: Weight gain ≤ 5 kg

G3: Weight gain ≥ 20 kg

Finland, hospital

Total weight gain: Routine prenatal care or maternity records

357

(P < 0.005 compared to G1)

Prepregnancy weight 20% over or under ideal body weight for height and normal weight

Poor

Jensen et al., 200559

Pregravid weight: Self-report

Infant BW for groups defined by GWG

G1: 3,456 g ± 620

G2: 3,624 g ± 675

G3: 3,757 g ± 582

G4: 3,784 g ± 597

N/A

Denmark, university hospitals

Total weight gain: Routine prenatal care or maternity records

G1: GWG < 5.0 kg

G2: GWG 5.0-9.9 kg

G3: GWG 10-14.9 kg

G4: GWG ≥ 15.0 kg

481

P < 0.0001

Obese

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Shapiro et al., 200094

Pregravid weight: Routine prenatal care

Infant BW for groups defined by BMI and weight gain

G1: 3,363 g

G2: 3,636 g

G3: 3,565 g

G4: 3,774 g

N/A

USA, community hospital

Total weight gain: Routine prenatal care or maternity records

159

G1: Low BMI (< 25), Low gain (< 35 lbs)

G2: Low BMI (< 25), High gain (> 35 lbs)

G3: High BMI (> 25), Low gain (< 35 lbs)

G4: High BMI (> 25), High gain (> 35 lbs)

All weight/BMI

Poor

β unstandardized coefficient from multiple regression; BMI, body mass index; BW, birthweight; cm, centimeters; g, grams; GWG, gestational weight gain; kg, kilogram; lbs, pounds; N/A, not applicable; NR, not reported; RCT, randomized controlled trial; SC, standardized coefficient; SD, standard deviation.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

born to women who gained < 35 lbs. One study among morbidly obese women (BMI > 35) found a similar trend, although it was inconsistent at the extremes of weight gain. Specifically, the following infant birthweights were found for each of the gestational weight gain categories: weight loss or 0 lbs, 3,302 g; 1-15 lbs, 3,192 g; 16-25 lbs, 3,337 g; 26-35 lbs, 3,506 g; > 35 lbs, 3,453 g.


Results for continuous total weight gain Fourteen studies (Table 12) evaluated the relationship between continuous total weight gain and birth-weight using linear regression techniques to determine the effect of every 1 kg increase in weight gain.48,55,59,90,92,93,96,98,100-105 Of these studies, three48,98,103 were rated of good quality, eight55,92,93,100-102,104,105 of fair quality, and three59,90,96 of poor quality. Seven studies of good and fair quality reported that birthweight increased between 16.7 and 22.6 g for every 1 kg increase in weight gain.48,93,98,101-103,105 Three poor-quality studies reported that birthweight increased between 18.4 and 44.3 g for every 1 kg increase in weight gain.59,90,96

Two studies of fair quality reported these values by BMI status.55,104 One found that 1 kg increases in weight gain among normal-weight women were associated with a 15 g increase in infant birthweight and, among obese women, an 11 g increase in infant birthweight.55 The other study reported, for each 1 kg increase in gestational weight gain, a 44.9 g increase in birth-weight for underweight women, a 22.9 g increase for women of normal weight, and an 11.9 g increase for overweight women.104

In the one fair-quality study that stratified by GDM, the association of total weight gain and infant birthweight was stronger among mothers with GDM than among women not diagnosed with GDM.100 Specifically, 1 kg increases in weight gain raised infant birthweight by 27.8 g among nondiabetic mothers and by 39.5 g among mothers with GDM.

Several studies reported statistically significant correlations between gestational weight gain and infant birthweight. Correlation coefficients between birthweight and total weight gain ranged from 0.22 to 0.28 in two fair-quality studies.97,105 A poor-quality study among obese, glucose-tolerant women reported a nonsignificant correlation value of r2 = 0.062.91


Results for continuous total weight gain by trimester Three studies reported on the effects of gestational weight gain, by trimester, on infant birthweights (Table 13).98,101,105 One U.S. study (rated good quality) reported that weight gain during the first trimester was associated with a 31 g increase in birthweight per kg of gestational weight gain. Comparable gains in infant birthweight for each kg of gestational weight gain in the second and third trimesters were 26 g and 7 g.98 This study also found that infant birthweight decreased by 211 g among mothers who lost weight during the first trimester.98

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 12. Total Gestational Weight Gain (continuous) and Infant Birthweight

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Brown et al., 200298

Pregravid weight: Measured by study investigators

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 20 g (P < 0.0001)

Maternal age, parity, pregravid BMI, height, infant sex, gestational age

USA, primary care clinics

Total weight gain: Collected by study investigators

389

All weight/BMI

Good

Groff et al., 1997103

Pregravid weight: Self-report 82% First prenatal visit 18%

G1: Increase in birthweight per 1 lb increase in total pregnancy weight gain

G1: β = 10.1g ± 1.76 (P ≤ 0.001)

Pregravid BMI, infant sex, smoking

USA, multispecialty clinics

Total weight gain: Routine prenatal care or maternity records

341

All weights/BMI

Good

Kieffer et al., 200648

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 19.7 g ± 2.8 (P < 0.01)

Parity, pregravid BMI, height, 1-hour glucose value, gestational age

USA, community health center

Total weight gain: Routine prenatal care or maternity records

1,041

All weights/BMI

Good

Abrams et al., 1995101

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 22.6 g (P < 0.001)

Maternal age, parity, pregravid BMI, height, smoking, infant sex, gestational age

USA, university hospital

Total weight gain: Routine prenatal care or maternity records

4,420

Nonobese

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Butte et al., 200397

Pregravid weight: Measured by study investigators

G1: Correlation coefficient

G2: Variability in birthweight accounted for by gestational age, pregravid weight, and total pregnancy weight gain

G1: 0.28

G2: 37.9%

Maternal race, pregravid BMI, gestational age

USA, US Agriculture

Total weight gain: Measured by study investigators

Research Service Children’s Nutrition Research Center

63

All weights/BMI

Fair

Edwards et al., 199655

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain for obese women

G1: β = 11 g ± 2 (P ≤ 0.001)

G2: β = 15 g ± 2 (P ≤ 0.001)

Maternal age, parity, pregravid BMI, pregnancy-induced hypertension, adequacy of prenatal care, alcohol use, drug use, smoking, gestational age

USA, hospital

Total weight gain: Routine prenatal care or maternity records

1,443

Normal and obese BMI

G2: Increase in birthweight per 1 kg increase in total pregnancy weight gain for normal weight women

Fair

Guihard-Costa et al., 200492

Pregravid weight: Routine prenatal care

G1: Standardized coefficient for effect of pregnancy weight gain on infant birthweight.

G1: SC = 0.199

Maternal age, parity, pregravid BMI, height

France, hospital database

Total weight gain: Routine prenatal care or maternity records

13,972

All weights/BMI

Standardized coefficients are regression coefficients calculated as if all of the independent variables had a variance of 1

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Hediger et al., 1994102

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 16.7 g ± 2.5 (P = 0.001)

Maternal age, maternal race/ethnicity, parity, pregravid weight, height, gestational age, prior poor outcome, fat loss, pregravid weight: low weight, fat accretion, smoking, infant sex

USA, setting not stated

Total weight gain: Routine prenatal care or maternity records

608

All weights/BMI

Fair

Kirchengast and Hartmann, 200393

Pregravid weight: Estimated from measured weight at first prenatal visit

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 17.32 (14.62, 20.03)

Maternal age, age at menarche, pregravid weight, height, distantia cristarum

Austria, university hospital

Total weight gain: Routine prenatal care or maternity records

8,011

All weights/BMI

Fair

Luke et al., 1996104

Pregravid weight: Self-report

Increase in birthweight per 1 kg increase in total pregnancy weight gain for BMI categories:

G1: β = 44.9 g ± 6.8 (P < 0.01)

G2: β = 22.9 g ± 3.9 (P < 0.01)

G3: β = 11.9 g ± 5.2 (P < 0.05)

Maternal age, parity, black ethnicity, smoking, gestational age, infant sex

USA, clinic

Total weight gain: Routine prenatal care or maternity records

487

All weights/BMI

Fair

G1: Underweight

G2: Normal weight

G3: Overweight

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Muscati et al., 1996105

Pregravid weight: Medical records

G1: Increase in birthweight per 1 kg increase in total weight gain up to week 20

G1: β = 22 g ± 6 (P < 0.01)

Parity, pregravid standard weight, pregravid excess weight, birth length, infant sex

Canada, public health department

Total weight gain: Collected by study investigators

371

All weight/BMI

Fair

Pezzarossa et al., 1996100

Pregravid weight: Self-report

Increase in birthweight per 1 kg increase in total pregnancy weight gain for:

G1: β = 27.8 g (P = 0.0001)

G2: β = 39.5 (P = 0.0001)

Pregravid BMI, fasting plasma glucose

Italy, not stated

Total weight gain: Routine prenatal care or maternity records

192

All weights/BMI

G1: Controls (normal glucose tolerance)

G2: GDM

Fair

Di Cianni et al., 200491

Pregravid weight: Not reported

 

F statistic = 3.16, P = 0.08

Pregravid BMI, maternal triglycerides, plasma glucose

Italy, diabetes clinic

Total weight gain: Collected by study investigators

 

180

All weights/BMI

Poor

Jensen et al., 200559

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 18.4 g (P < 0.001)

Maternal age, pregravid BMI, smoking, gestational age, result of 2-hour oral glucose tolerance test

Denmark, university hospitals

Total weight gain: Routine prenatal care or maternity records

481

Obese

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Paauw et al., 200590

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in total pregnancy weight gain

G1: β = 21.0 g

Maternal race, pregravid weight, marital status, smoking, gestational age

USA, hospital

Total weight gain: Self-report

351

All weights/BMI

Poor

Springer et al., 199296

Pregravid weight: Self-report

G1: Increase in birthweight per 1 lb increase in total pregnancy weight gain

G1: β = 20.1g

Maternal age, pregravid weight, length of gestation, smoking, weight gain at 20 weeks

USA, university hospital

Total weight gain: Routine prenatal care or maternity records

107

All weights/BMI

Poor

AGA, Appropriate for gestational age; β, unstandardized coefficient from multiple regression; BMI, body mass index; g, gram; GDM, gestational diabetes mellitus; kg, kilogram; lb, pound; LGA, large-for-gestational age; NR, not reported.

A Canadian study of fair quality found similar results: for each 1 kg increase in weight gain up to week 20, birthweight increased by 22 g; increases from week 21 to 30 increased birthweight by 31 g; and weight gain from week 31 to term increased birthweight by 12 g.105 Lastly, another U.S. study of fair quality reported an 18 g increase in birthweight for each kilogram gained by the mother in the first trimester. Corresponding increases in the second and third trimesters were 32.8 g and 17.0 g, respectively.101


Results from other measures of weight gain (net weight gain and proportional weight gain) Four studies examined the associations between infant birthweight and various other measures of gestational weight gain. Three studies (1 rated poor quality) of net weight gain (total gestational weight gain minus infant birthweight) showed that infant birthweight increased as net gestational weight gain increased (Table 14).70,83,104 In one study, for every 1 kg increase in net weight gain, birthweight rose by 15.4 g.70 In another, which examined differences by BMI status, increases of 1 kg

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 13. Continuous Gestational Weight Gain by Trimester and Infant Birthweight

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Brown et al., 200298

Pregravid weight: Measured by study investigators

G1: Increase in birthweight per 1 kg increase in first trimester weight gain

G2: Increase in birthweight per 1 kg increase in second trimester weight gain

G3: Increase in birthweight per 1 kg increase in third trimester weight gain

G1: β = 31 g (P < 0.0007)

Maternal age, parity, pregravid BMI, height, infant sex, gestational age

USA, primary care clinics

Total weight gain: Collected by study investigators

G2: β = 26 g (P < 0.007)

389

All weight/BMI

G3: β = 7 g (P < 0.40)

Good

Abrams et al., 1995101

Pregravid weight: Self-report

G1: Increase in birthweight per 1 kg increase in first trimester weight gain

G2: Increase in birthweight per 1 kg increase in second trimester weight gain

G3: Increase in birthweight per 1 kg increase in third trimester weight gain

G1: β = 18.0 g ± 2.4 (P < 0.001)

Maternal age, parity, pregravid BMI, height, smoking, infant sex, gestational age

USA, university hospital

Total weight gain: Routine prenatal care or maternity records

G2: β = 32.8 g ± 2.8 (P < 0.001)

4,420

Nonobese

Fair

G3: β = 17.0 g ± 2.9 (P < 0.001)

Muscati et al., 1996105

Pregravid weight: Medical records

G1: Increase in birthweight per 1 kg increase in total weight gain from weeks 21 to 30

G2: Increase in birthweight per 1 kg increase in total weight gain from weeks 31 to term

G1: β = 31 g ± 7 (P < 0.001)

Parity, pregravid standard weight, pregravid excess weight, birth length, infant sex

Canada, public health department

Total weight gain: Collected by study investigators

G2: β = 12 g ± 6 (P < 0.05)

371

All weight/BMI

Fair

β, unstandardized coefficient from multiple regression; BMI, body mass index; g, gram; kg, kilogram; lbs, pounds.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

in net weight gain raised infant birthweight as follows: for underweight women, 41.9 g; for women of normal weight, 19.2 g; and for obese women, 9.1 g.104 Each kilogram of net weight gain associated with an increase of 111.2 g in birthweight in another study.83

The fourth study, which considered proportional gestational weight gain (total gestational weight gain divided by pregravid weight) found that for mothers with BMIs of 19.5 to 22.4, those who gained above the median proportional gestational weight gain had infants who were 322 g heavier than the infants of mothers who gained below the median.

Similar results were found for mothers with BMIs of 22.4 to 28.5: those who gained above the median gave birth to infants who were 225 g heavier. Finally, for women with BMIs above 28.5, the increase in birthweight was 232 g.75

Low birthweight

Study characteristics Thirteen studies examined the effect of gestational weight gain on low birthweight (LBW) (Evidence Table 19).2,4,52,54,70,71,75,93,95,106-109 LBW is defined as infant birthweight < 2,500 g. Overall, the risk of LBW decreased as gestational weight gain increased. In general, risks for LBW began to decrease for gestational weight gains above 25 to 30 pounds. In 11 of these studies, the analyses were adjusted for multiple confounders, including maternal age, pregravid BMI, smoking, alcohol use, gestational age, parity, race, marital status, maternal education, pregnancy complications, and infant sex.2,4,52,70,71,75,93,106-109


Overview of results Ten studies considered the relationship between LBW and total gestational weight gain (Table 15).2,4,52,54,71,93,106-109 One of these studies was rated good quality,106 seven of fair quality,2,4,52,71,93,107,108 and two of poor quality.54,109 In general, as gestational weight gain increased, LBW decreased.

Three studies evaluated measures of gestational weight gain other than total gestational weight gain (Table 16).70,75,95 Two70,75 studies were of fair quality and one95 was of poor quality. These studies suggest reduced risk of LBW in association with increases in net, proportional, or other measures of change in weight gain.

Results for total gestational weight gain and LBW Results taken from a figure from a good-quality study of low-income black and Hispanic women showed the trend of decreasing LBW as maternal weight near term compared to the standard weight-for-height increased.106 A population-based cohort study in New York City reported a protective effect for LBW (OR, 0.41; 95% CI, 0.39-0.43) for women who gained more than 41 pounds compared with women who gained less than 41 pounds.71 A study in Denmark found that the risk of LBW was significantly reduced only for

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 14. Net and Proportional Gestational Weight Gain and Infant Birthweight

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Johnson et al., 199270

Pregravid weight: Self-report

G1: Increase in birthweight per 1 lb increase in net pregnancy weight gain

USA, prenatal clinics

3,191

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Fair

Luke et al., 1996104

Pregravid weight: Self-report

Increase in birthweight per 1 kg increase in net pregnancy weight gain for BMI categories:

USA, clinic

487

Total weight gain: Routine prenatal care or maternity records

G1: Underweight

G2: Normal weight

G3: Overweight

All weights/BMI

Fair

Shepard 199875

Pregravid weight: Self-report

Infant birthweight for mothers with:

USA, obstetrical practices in New Haven, CT

G1: Low average BMI (19.5 to 22.4), proportional weight gained > median

G2: Low average BMI (19.5 to 22.4), gained < median

G3: High average BMI (22.5 to 28.5), gained > median

G4: High average BMI (22.5 to 28.5), gained < median

G5: Obese (> 28.5 BMI), gained > median

G6: Obese (> 28.5 BMI), gained < median

Total weight gain: Routine prenatal care or maternity records

2,301

All weights/BMI

Fair

Velonakis et al., 199783

Pregravid weight: Self-report

G1: Increase in birthweight for net pregnancy weight gain

France, hospital

2,040

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Poor

β, unstandardized coefficient from multiple regression; BMI, body mass index; C-section, cesarean section; g, gram; kg, kilogram; lbs, pounds; N/A, not applicable.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: β = 15.4 g ± 2.2 (P < 0.0001)

Maternal race, parity, pregravid BMI, height, pregravid weight, marital status, education, tobacco/alcohol/drug use, pregnancy-induced hypertension, gestational age, macrosomia, infant sex

G1: β = 41.9 g ± 7.5 (P < 0.01)

G2: β = 19.2 g ± 3.9 (P < 0.01)

G3: β = 9.1 g ± 5.3

Maternal age, parity, black ethnicity, smoking, gestational age, infant sex

G1: 3,231 g

G2: 3,553 g

G3: 3,395 g

G4: 3,620 g

G5: 3,685 g

G6: 3,453 g

N/A

G1: β = 111.17 g ± 12.94 (P = 0.000)

Maternal age, parity, pathology of previous/current pregnancy, previous diseases, reproductive history, marital status, employment, infant sex, height, weight, smoking, alcohol use, APGAR score, gestational age, nationality

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 15. Total Gestational Weight Gain and Low Birthweight (LBW)

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Hickey et al., 1990106

Pregravid weight: Self-report

G1: Percent BW < 3,000, Low weight gain < 120% of standard

G2: Percent BW ≥ 3,000, Low weight gain < 120% of standard

G3: Percent BW < 3,000, Acceptable weight gain ≥ 120% of standard

G4: Percent BW ≥ 3,000, Acceptable weight gain ≥ 120% of standard

United States, prenatal clinics

Total weight gain: Routine prenatal care or maternity records

325

All weights/BMI

Good

Cogswell et al., 19942

Pregravid weight: Self-report

ORs and 95% CI, for LBW by GWG and prepregnancy BMI

USA, Pregnancy Nutrition Surveillance System

Total weight gain: Self-report

G1: Normal BMI, GWG < 15 lbs

G2: Normal BMI, GWG ≥ 40 lbs

G3: Normal BMI, GWG 25-29 lbs (Reference for normal BMI)

G4: Overweight BMI, GWG 30-34 lbs

G5: Overweight BMI, GWG 35-39

G6: Overweight BMI, GWG ≥ 40 lbs

G7: Overweight BMI, GWG 15-19 lbs (Reference for overweight BMI)

53,541

Normal/Overweight/Obese

Fair

Desjardins and Hardwick, 1999107

Pregravid weight: Self-report

G1: OR and 95% CI, for LBW and inadequate weight gain (defined by dietician)

Canada, Healthiest Babies Possible Program

Total weight gain: Home visitor’s scale

1,892

All weights/BMI

Fair

Kiel et al., 20074

Pregravid weight: Medical records

G1: Odds of LBW for weight gain > 25 lbs

G2: OR of LBW for weight gain < 15 lbs

G3: Reference Weight gain 15-25 lbs

USA, birth certificate registry

Total weight gain: Routine prenatal care or maternity records

120,251

Obese

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 38.2

G2: 61.8

G3: 22.1

G4: 77.9

N/A

G1: 2.1 (1.6-2.6)

G2: 0.5 (0.4-0.6)

G3: 1.0

G4: 0.5 (0.3-0.8)

G5: 0.6 (0.3-1.1)

G6: 0.4 (0.3-0.7)

G7: 1.0

Maternal age, maternal race, height, smoking, infant sex, gestational age

G1: 1.15 (0.78-1.67)

Gestational age, adolescence, pregravid underweight, number of Healthiest Baby Possible visits

G1: Odds of LBW are lower for women in this group

G2: Odds of LBW are higher for women in this group

Numerical value for ORs not reported in study

Maternal age, maternal race, maternal education, poverty, smoking, parity, chronic hypertension

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Kirchengast and Hartmann, 200393

Pregravid weight: Estimated from measured weight at first prenatal visit

G1: OR and 95% CI, for LBW

Austria, university hospital

8,011

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Fair

Murakami et al., 200452

Pregravid weight: Self-report

OR and 95% CI, for LBW

G1: GWG < 8.5 kg

G2: GWG 8.5-12.5 kg

G3: GWG > 12.5 kg

Japan, hospital

Total weight gain: Routine prenatal care or maternity records

633

All weights/BMI

Fair

Rosenberg et al., 200571

Pregravid weight: Self-report

OR and 95% CI, for LBW

G1: GWG ≥ 41 lbs

G2: GWG < 41 lbs

USA, vital statistics data

Total weight gain: Routine prenatal care or maternity records

329,988

All weights/BMI

Fair

Zhou and Olsen, 1997108

Pregravid weight: Self-report

OR and 95% CI, for LBW for GWG categories by BMI

Denmark, two communities

Total weight gain: Routine prenatal care or maternity records

G1: GWG < 11 kg, Underweight (Reference)

G2: GWG < 11 kg, Normal weight

G3: GWG < 11 kg, Overweight

G4: GWG 12-15 kg, Underweight

G5: GWG 12-15 kg, Normal weight

G6: GWG 12-15 kg, Overweight

G7: GWG ≥ 16 kg, Underweight

G8: GWG ≥ 16 kg, Normal weight

G9: GWG ≥ 16 kg, Overweight

7,122

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 0.90 (0.85-0.95)

Maternal age, pregravid weight, height, distantia cristarum

G1: 1.26 (0.57-2.75)

G2: Reference

G3: 0.62 (0.24-1.62)

Maternal age, parity, pregravid BMI, smoking, gestational age

G1: 0.41 (0.39-0.43)

G2: Reference

Maternal age, parity, GDM, pregnancy-induced hypertension, preeclampsia, pregravid weight, chronic diabetes, chronic hypertension, marital status, maternal education, mother’s birthplace, prenatal care payer, social risk, trimester prenatal care began

G1: 1.0

G2: 0.9 (0.5-1.5)

G3: 0.8 (0.3-2.0)

G4: 0.5 (0.2-1.0)

G5: 0.8 (0.4-1.5)

G6: 0.9 (0.2-3.8)

G7: 0.3 (0.1-1.0)

G8: 0.4 (0.2-0.8)

G9: 0.0 (0.0-2,500)

Maternal age, parity, alcohol, no diabetes, term delivery, smoking, infant sex, gestational age

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Bianco et al., 199854

Pregravid weight: Self-report

% LBW for GWG:

USA, medical center

G1: Weight loss or 0 lbs

G2: 1-15 lbs

G3: 16-25 lbs

G4: 26-35 lbs

G5: > 35 lbs

613

Total weight gain: Routine prenatal care or maternity records

Morbidly obese (BMI > 35)

Poor

Lasker et al., 2005109

Pregravid weight: Not stated

OR and 95% CI, for LBW

USA, hospital

G1: GWG < 10 lbs

G2: GWG > 30 lbs

G3: GWG 21-30 lbs (Reference)

5,528

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Poor

BMI, body mass index; BW, birthweight; CI, confidence interval; GDM, gestational diabetes mellitus; GWG, gestational weight gain; kg, kilogram; lbs, pounds; LBW, low birthweight; N/A, not applicable; OR, odds ratio.

underweight women gaining at least 12 kg when compared to underweight women gaining less than 11 kg (OR, 0.5; 95% CI, 0.2-1.0).108 A study in Austria93 found that the odds ratio of LBW was 0.9 (95% CI, 0.85-0.95) for each 1 kg increase in gestational weight gain. A study among obese women also found that the risk of having a LBW infant was increased for low gestational weight gains.4

Among low-income women the effect of weight gain varied by pregravid BMI;2 only among women of average weight was there a consistent decrease in LBW risk as gestational weight gain increased from < 15 pounds to ≥ 40 pounds. Mothers of average weight who gained less than 15 pounds had an OR for delivering an LBW infant of 2.1 (95% CI, 1.6-2.6). The odds of LBW were substantially lower for women who gained more than 40 pounds (OR, 0.5; 95% CI, 0.4-0.6). There was no reduction in the percentage of LBW infants for weight gains above 30 to 34 pounds for overweight women, and for weight gains above 15 to 19 pounds for obese women. For overweight women gaining 30 to 34 pounds, the OR was 0.5 (95% CI, 0.3-0.8). The poor-quality studies showed results in the same general direction.54,109

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 2

G2: 11.1

G3: 8.3

G4: 5.2

G5: 3.8

N/A

G1: 2.43 (1.45-4.05)

G2: 0.63 (0.47-0.85)

G3: 1.00

Maternal age, maternal race, marital status, prenatal care, prior term births, prior abortions, prior preterm births, BMI at delivery, preeclampsia, bleeding, smoking, multiple births, premature birth, congenital anomaly, incompetent cervix, smoking

Two fair-quality studies did not find a statistically significant association between total gestational weight gain and LBW, although the point estimates were in the expected direction.52,107 Among a cohort of Japanese women,52 for weight gain < 8.5 kg, the adjusted OR of LBW was 1.26 (95% CI, 0.57-2.75) and for weight gain > 12.5 kg, it was 0.62 (95% CI, 0.24-1.62), when these groups were compared with women gaining between 8.5 and 12.5 kg. Another study found that inadequate weight gain was associated with an OR for LBW of 1.15 (95% CI, 0.78-1.67);107 in this study, a dietitian determined inadequate weight gain status (exact criteria were not reported).


Results for net, proportional, or other measures of change in weight gain and LBW One study looked at the relationship between net weight gain (total gestational weight gain minus infant birthweight) and the risk of LBW; the risk decreased as net weight gain increased.70 Odds ratios reported are in comparison with women gaining < 14.9 pounds. For mothers gaining > 33 pounds, the OR was 0.38 (95% CI, 0.2-0.8); for women gaining 24 to 33 pounds, the OR was 0.54 (95% CI, 0.28-1.04); and for women

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 16. Other Gestational Weight Gain Measures and LBW

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Johnson et al., 199270

Pregravid weight: Self-report

OR and 95% CI, for LBW

USA, prenatal clinics

G1: Net WG < 14.9 lbs (Reference)

G2: Net WG 14.9-23.5 lbs

G3: Net WG 24-33 lbs

G4: Net WG > 33 lbs

Total weight gain: Routine prenatal care or maternity records

3,191

All weights/BMI

Fair

Shepard, 199875

Pregravid weight: Self-report

%LBW

USA, obstetrical practices in New Haven, CT

G1: Proportional WG < median, underweight (BMI < 19.4)

G2: Proportional WG < median, obese (BMI > 28.5)

G3: Proportional WG > median, underweight (BMI < 19.4)

G4: Proportional WG > median, Low-average BMI (19.5-22.4)

G5: Proportional WG > median, High-average BMI (22.5-28.5)

G6: Proportional WG > median, obese (BMI > 28.5)

Total weight gain: Routine prenatal care or maternity records

2,301

All weights/BMI

Fair

Cherry et al., 199395

Pregravid weight: Measured by study investigators

%LBW for each shifting of EW category.

USA, hospital

599

Light: < 90% EW

Normal: 90 to 110% of EW

Heavy: > 110% EW

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Poor

G1: Heavy to normal

G2: Normal to light

G3: Normal to heavy

G4: Light to normal

BMI, body mass index, CI, confidence interval; EW, expected weight; lb, pound; LBW, low birthweight; N/A, not applicable; OR, odds ratio; WG, weight gain.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 1.0 (Reference)

G2: 0.51 (0.27-0.98)

G3: 0.54 (0.28-1.04)

G4: 0.38 (0.2-0.8)

Maternal race, parity, pregravid BMI, height, pregravid weight, marital status, education, tobacco/alcohol/drug use, pregnancy-induced hypertension, gestational age, macrosomia, infant sex

G1: 3.5%

G2: 7.4%

G3: 2.1%

G4: 2.8%

G5: 2.1%

G6: 4.6%

N/A

G1: 5%

G2: 32%

G3: 3.1%

G4: 2.7%

N/A

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

gaining 14.9 to 23.5 pounds, the OR was 0.51 (95% CI, 0.27-0.98). The association between risk of LBW infants and proportional weight gain (total gestational weight gain divided by pregravid weight) above and below the median was also evaluated in relation to BMI status.75 Obese women had a higher percentage of LBW infants than underweight women. The risk of LBW was even higher for women gaining less than the median.

A study of adolescent mothers (rated poor quality) showed similar effects. Mothers who shifted to lower weight classes during pregnancy were more likely to have LBW babies, and mothers who progressed to higher weight classes had lower percentages of LBW.95

Macrosomia

Study characteristics Twelve studies examined the influence of gestational weight gain on macrosomia in their infants (Evidence Table 20).2,4,49,59,70,77,93,108,110-113 Studies did not define macrosomia consistently. Four studies defined macrosomia as birthweight > 4,500 g.2,108,110,113 Seven of the remaining eight studies defined macrosomia as birthweight > 4,000 g.4,59,70,77,93,111,112 One study applied both definitions.49 One110 study was rated to be of good quality, nine2,4,70,77,93,108,111-113 of fair quality, and two49,59 of poor quality.


Overview of results In four studies (all fair2,108,110,113) defining macrosomia as birth > 4,500 g and seven (6 fair4,70,77,93,111,112 and 1 poor59) studies defining macrosomia as birthweight > 4000 g, the highest weight gains were demonstrated to be associated with macrosomia. A single poor study failed to show a significant association, using either definition of macrosomia.49


Detailed results In four of the studies in which macrosomia was defined as birthweight > 4,500 g,2,108,110,113 the highest weight gains were associated with increased risk of macrosomia (Table 17). These four studies adjusted for multiple confounders such as age, BMI, race, parity, glucose levels, placental weight, smoking status, gestational age, and infant sex.2,108,110,113 A nested case-control study (rated good quality), using women gaining 0.22 to 0.31 kg per week as the reference group, found that women with the highest rates of pregnancy weight gain (0.40 to 1.03 kg/week) were at increased risk for macrosomia (OR, 2.23; 95% CI, 1.54-3.22) and that women with the lowest rates (−0.26 to 0.21 kg/week) were at decreased risk (OR, 0.52; 95% CI, 0.34-0.79).110 Results were similar when considering rates of weight gain only before 24 to 28 weeks of gestation.

A fair-quality study in Denmark also showed increased risk of macrosomia at the highest weight gains, with the highest risks among overweight

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 17. Gestational Weight Gain and Macrosomia > 4,500 g

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Hedderson et al., 2006110

Pregravid weight: Self-report

ORs and 95% CI, for macrosomia based on rate of weight gain

G1: 0.52 (0.34-0.79)

G2: 1.00

G3: 0.99 (0.67-1.47)

G4: 2.23 (1.54-3.22)

Maternal age, maternal race/ethnicity, parity, pregravid BMI, screening glucose value, gestational age

USA, Kaiser Permanente Medical Care Program

Total weight gain: Routine prenatal care or maternity records

Rate of gain kg/wk:

G1: −0.26 to 0.21

G2: 0.22 to 0.31 (Reference)

G3: 0.32 to 0.39

G4: 0.40 to 1.03

45,245

All weights/BMI

Good

Clausen et al., 2005113

Pregravid weight: Routine prenatal care

ORs and 95% CIs for macrosomia

G1: 1.0

G2: 2.1 (0.8-5.1)

G3: 3.5 (1.5-8.0)

G4: 4.3 (1.9-9.8)

Maternal age, parity, smoking, placental weight, gestational diabetes, first trimester BMI

Norway, university hospital

G1: WG, Quartile 1 (Reference)

G2: WG, Quartile 2

G3: WG, Quartile 3

G4: WG, Quartile 4

2050

Total weight gain: Routine prenatal care of maternity records

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Cogswell et al., 19942

Pregravid weight: Self-report

ORs and 95% CIs for macrosomia by GWG and prepregnancy BMI

G1: 1.0

G2: 1.5 (1.0-2.3)G3: 3.3 (2.3-4.7)

G4: 1.0

G5: 4.0 (1.6-10.1)

G6: 1.0

G7: 1.9 (1.3-2.9)

G8: 2.1 (1.3-3.2)

G9: 2.3 (1.6-3.3)

Maternal age, maternal race, height, smoking, infant sex, gestational age

USA, Pregnancy Nutrition Surveillance System

Total weight gain: Self-report

G1: Normal BMI, GWG 25-29 lbs (Reference for normal BMI)

G2: Normal BMI, GWG 35-39 lbs

G3: Normal BMI, GWG ≥ 40 lbs

G4: Overweight BMI, GWG 15-19 lbs (Reference for overweight BMI)

G5: Overweight BMI, GWG ≥ 40 lbs

G6: Obese, GWG 15-19 lbs (Reference for obese GMI)

G7: Obese BMI, GWG 30-34 lbs

G8: Obese BMI, GWG 35-39 lbs

G9: Obese BMI, GWG ≥ 40 lbs

53,541

Normal/Overweight/Obese

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Zhou and Olsen, 1997108

Pregravid weight: Self-report

OR and 95% CI, for macrosomia by GWG categories and BMI

G1: 1.0

G2: 52.8 (0.3-22.9)

G3: 9.7 (1.2-81.8)

G4: 0.0 (0.0-7×105)

G5: 6.8 (0.9-51)

G6: 27.1 (3.3-220)

G7: 6.1 (0.7-52.5)

G8: 15.7 (2.2-114)

G9: 45.6 (6.0-349)

Maternal age, parity, alcohol, no diabetes, term delivery, smoking, infant sex, gestational age

Denmark, two communities

Total weight gain: Routine prenatal care or maternity records

G1: GWG < 11 kg, underweight (Reference)

G2: GWG < 11 kg, normal weight

G3: GWG < 11 kg, overweight

G4: GWG 12-15 kg, underweight,

G5: GWG 12-15 kg, normal weight

G6: GWG 12-15 kg, overweight

G7: GWG ≥ 16 kg, underweight

G8: GWG ≥ 16 kg, normal weight

G9: GWG ≥ 16 kg, overweight

7,122

All weights/BMI

Fair

Brennand et al., 200549

Pregravid weight: Medical records

% Macrosomia among obese women only

G1: 16.9%

G2: 15.3%

G3: 18.4%

(P = 0.834)

 

N/A

Canada, medical records

Total weight gain: Routine prenatal care or maternity records

G1: Low WG, < 7 kg

G2: Acceptable WG, 7-11.5 kg

G3: Excessive WG, > 11.5 kg

603

Normal/Overweight/Obese

Poor

BMI, body mass index; CI, confidence interval; GWG, gestational weight gain; kg, kilogram; kg/wk, kilogram per week; N/A, not applicable; OR, odds ratio; wk, week.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

and obese women.108 However, the confidence intervals from this study are very imprecise. A fair-quality study in Norway showed similar results, with increasing ORs as weight gain increased. Women with weight gain in the fourth quartile, as compared to weight gain in the first quartile, had the highest OR of 4.3 (95% CI, 1.9-9.8).113

Among low-income women enrolled in the Supplemental Food Program for Women, Infants, and Children (WIC), a fair-quality U.S. study reported significant associations between weight gain and macrosomia only for women gaining more than 30 to 34 pounds when compared with women gaining 25 to 29 pounds for women of normal weight or with women gaining 5 to 19 pounds for overweight and obese women.2 For average-weight women, the OR was 1.5 (95% CI, 1.0-2.3), for those gaining 35 to 39 pounds and 3.3 (95% CI, 2.3-4.7) for women gaining 40 pounds or more. Overweight women also had high risks for macrosomia, but only at weight gains of 40 pounds or more (OR, 4.0; 95% CI, 1.6-10.1). The OR among obese women gaining 30 to 34 pounds was 1.9 (95% CI, 1.3-2.9). Similar results were found for obese women gaining more than 35 pounds with odds ratios ranging from 2.1 to 2.3.

In a U.S. study of Cree women (rated poor quality), weight gain among obese women was not significantly associated with macrosomia.49

Of the eight studies that considered macrosomia as > 4,000 g, seven found a significant association between gestational weight gain and macrosomia (Table 18).4,59,70,77,93,111,112 In general, the highest weight gains were associated with an increased risk of macrosomia. Six4,70,77,93,111,112 of these studies were rated of fair quality, and one59 of poor quality. These studies were adjusted for multiple confounders including maternal age, race, education, parity, height, pregravid weight, pregravid BMI, distantia cristarum, length of gestation, glucose levels, smoking status, and infant sex.

Among the fair-quality studies of gestational weight gain on macrosomia, ORs for this association were between 2.41 and 3.37 for the highest weight gains when compared to weight gains within the normal range.70,77,111,112 Among a cohort of Japanese women (fair-quality study), the group with total weight gain above the 90th percentile for gestational age had an OR for macrosomia of 2.41 (95% CI, 1.83-3.17) relative to the group in the 50th to 74th percentile.111 The effect was reduced for total weight gain based on percentile for gestational age for the lower percentile ranges. A fair-quality U.S. study looked at the association between net weight gain (total gestational weight gain minus infant birthweight) and macrosomia.70 With women gaining < 14.9 pounds as the reference group, the strongest effect was noted among women gaining > 33 pounds (OR, 2.86; 95% CI, 2.02-4.02), followed by women gaining 24 to 33 pounds (OR, 1.77; 95% CI, 1.24-2.52); no significant effect was observed for women gaining 14.9 to 23.5 pounds. A fair-quality study in Germany found

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 18. Gestational Weight Gain and Macrosomia > 4,000g

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Bergmann et al., 2003112

Pregravid weight: Not stated

ORs and 95% CIs of macrosomia

G1: 1.0

G2: 1.85 (1.77-1.93)

G3: 3.37 (3.22-3.53)

Pregravid BMI, height, parity, smoking, diabetes, postterm delivery

Germany, Berlin Perinatal Registry

Total weight gain: Not stated

G1: WG < 10 kg (Reference)

G2: WG 10-16 kg

G3: WG ≥ 16 kg

206,308

All weights/BMI

Fair

Jain et al., 200777

Pregravid weight: Not stated

ORs and 95% CIs for macrosomia

G1: 0.49 (0.30-0.82)

G2: 1.0

G3: 1.17 (0.82-1.65)

G4: 2.83 (2.04-3.92)

Maternal age, pregravid BMI, parity, education, race/ethnicity, US/foreign origin

USA, birth certificate records and Pregnancy Risk Assessment Monitoring System

Total weight gain: Birth certificate

G1: WG ≤ 15 lbs

G2: WG 15-24 lbs

G3: WG 25-35 lbs

G4: WG ≥ 35 lbs

7,661

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Johnson et al., 199270

Pregravid weight: Self-report

OR and 95% CI, for macrosomia

G1: 1.0

G2: 1.20 (0.83-1.75)

G3: 1.77 (1.24-2.52)

G5: 2.86 (2.02-4.02)

Maternal race, parity, pregravid BMI, height, pregravid weight, marital status, education, tobacco/alcohol/drug use, pregnancy-induced hypertension, gestational age, macrosomia, infant sex

USA, prenatal clinics

Total weight gain: Routine prenatal care or maternity records

G1: Net WG < 14.9 lbs (Reference)

G2: Net WG 14.9-23.5 lbs

G3: Net WG 24-33 lbs

G4: Net WG > 33 lbs

3,191

All weights/BMI

Fair

Kiel et al., 20074

Pregravid weight: Medical records

G1: Odds of macrosomia for WG > 25 lbs

G2: OR of macrosomia for WG < 15 lbs

G3: Reference WG 15-25 lbs

G1: Odds of Macrosomia are higher for women in this group

G2: Odds of Macrosomia are lower for women in this group

Maternal age, maternal race, maternal education, poverty, smoking, parity, chronic hypertension

USA, birth certificate registry

Total weight gain: Routine prenatal care or maternity records

120,251

Obese

Fair

Numerical value for ORs not reported in study

Kirchengast and Hartmann, 200393

Pregravid weight: Estimated from measured weight at first prenatal visit

G1: OR and 95% CI, for Macrosomia

G1: 1.07 (1.05-1.10)

Maternal age, pregravid weight, height, distantia cristarum

Austria, university hospital

8,011

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Takimoto et al., 2006111

Pregravid weight: Medical records

ORs and 95% CI, for macrosomia

G1: 0.31 (0.20-0.47)

G2: 0.49 (0.34-0.70)

G3: 1.0

G4: 1.62 (1.24-2.12)

G5: 2.41 (1.83-3.17)

Maternal age, parity, pregravid weight, gestational age, infant sex

Japan, obstetric units

112,257

Total weight gain: Routine prenatal care or maternity records

G1: Total GWG < 25th percentile for GA

G2: Total GWG 25-49th percentile for GA

G3: Total GWG 50-74th percentile for GA (Reference)

G4: Total GWG 75-89th percentile for GA

G5: Total GWG ≥ 90th percentile for GA

All weights/BMI

Fair

Brennand et al., 200549

Pregravid weight: Medical records

% Macrosomia among obese women only

G1: 47.0%

G2: 42.9%

G3: 54.4%

(P = 0.234)

N/A

Canada, medical records

603

Total weight gain: Routine prenatal care or maternity records

G1: Low WG, < 7 kg

G2: Acceptable WG, 7-11.5 kg

G3: Excessive WG, > 11.5 kg

Normal/Over-weight/Obese

Poor

Jensen et al., 200559

Pregravid weight: Self-report

ORs and 95% CIs for Macrosomia

G1: 1.0

G2: 1.8 (0.8-3.8)

G3: 2.2 (1.0-4.7)

G4: 4.0 (1.8-9.0)

Maternal age, pregravid BMI, gestational age, 2-hour OGTT, parity, smoking, ethnicity, clinical center

Denmark, university hospitals

Total weight gain: Routine prenatal care or maternity records

G1: GWG < 5.0 kg (Reference)

G2: GWG 5.0-9.9 kg

G3: GWG 10.0-14.9 kg

G4: GWG ≥ 15.0 kg

481

Obese

Poor

BMI, body mass index; CI, confidence interval; GA, gestational age; GWG, gestational weight gain; lbs, pounds; OGTT, oral glucose tolerance test; OR, odds ratio; WG, weight gain.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

a higher risk of macrosomia for women gaining more than 16 kg as compared to women gaining less than 10 kg (OR, 3.37; 95% CI, 3.22-3.53).112 Similar results were noted in a fair-quality U.S. study where weight gains above 35 pounds (as compared to weight gains of 15 to 25 pounds) were associated with an OR for macrosomia of 2.83 (95% CI, 2.04-3.92).77 A fair-quality study in Austria found that for each 1 kg increase in gestational weight gain, the OR for macrosomia was 1.07 (95% CI, 1.05-1.10).93 Of the poor-quality studies, one found results in a similar direction.59 One poor-quality study among obese Cree women found that the percent macrosomia did not differ between weight gain groups.49

Size based on gestational age

Study characteristics Twenty-five articles from 23 studies examined the association between gestational weight gain and large-for-gestational-age (LGA) and small-for-gestational-age (SGA) infants.4,51,58,59,61,66,68,89,95,100,105,108,111,114-123 These investigators used various definitions to classify both LGA and SGA infants. Some defined LGA as birthweight greater than the 90th percentile or more than 2 standard deviations (SD) above the mean. Some defined SGA as birthweight less than the 10th (or 15th) percentile or more than 2 (or 1.5) SD below the mean.

Of the 14 articles addressing LGA (Evidence Table 21),4,54,58,59,61,68,100,105,115,116,118,120-122 two defined LGA using the > 2 SD criterion.58,120 Ten used the commonly applied 90th percentile definition;4,54,59,61,100,105,115,116,118,121 one study evaluated multiple percentiles;68 and one defined LGA as fetal growth ratio (FGR) > 1.15.122 FGR is the ratio of the observed birthweight at a given gestational age to the mean birthweight at a given gestational age for a certain fetal growth distribution.

SGA definitions varied considerably as well: birthweight < 10th percentile; < 2 (or 1.5) SD below the mean; FGR < 0.85; or a combination of birthweight and percentile of placenta weight. If a study used a definition other than birthweight < 10th percentile, the specific criterion used will be noted in the text below. In general, the lowest weight gains were associated with increased risks for SGA.


Overview of results for LGA Among the studies that did not use BMI status (Table 19), six100,105,115,118,121,122 were rated of fair quality and four54,59,68,120 of poor quality. All reported lower risks of LGA with lower gestational weight gain. Studies that stratify by BMI status present greater challenges to synthesis. Two studies (1 good116 and 1 fair58) examined a range of BMI categories, and found inconsistent results: one reported that the estimates of LGA did not differ greatly across BMI categories116 while the other reported that high weight gain (> 16 kg) was strongly associated with LGA, and this association was most pronounced in the lowest BMI

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

categories. A fair-quality study of obese women4 observed lower odds of LGA among women who gained less than the reference group (15-25 pounds) and higher odds of LGA among women who gained more the reference group. A poor-quality study among Japanese women found that nulliparous women in the highest weight gain category (> 0.40 kg/week) had ORs for LGA of 2.25 (95% CI, 1.03-4.94) for low BMI women and 2.58 (95% CI, 1.71-3.89) for medium BMI women.61


Detailed results Among the studies that did not use BMI status (Table 19), three fair-quality studies that evaluated the impact of a 1 kg increase in weight gain produced similar results.105,115,121 For Italian women, the OR of having an LGA infant was 1.08 (95% CI, 1.03-1.12).115 For nondiabetic Japanese women with a positive diabetic screen, the OR was 1.08 (95% CI, 0.81-1.44).121 The third study evaluated this relationship separately for weight gain by time: up to week 20, from week 21 to week 30, and from week 31 to term. It found ORs of 1.17, 1.16, and 1.02 (non-significant), respectively.105 The OR for weeks 31 to term was not significant. In other words, the odds of giving birth to an LGA infant tends to increase for each 1 kg increase in gestational weight gain during the first and second trimester.

Two fair-quality studies100,118 considered the association between categorical weight gain and LGA. In a U.S. study,118 women with the highest weight gains were at increased risk for LGA (OR, 1.89; 95% CI, 1.51-2.37) relative to women in the 25th to 75th percentile of weight gain and to women in the 10th to 90th percentile (OR. 1.87; 95% CI, 1.39-2.52). In a study involving mothers with GDM,100 the risks for LGA were similar for weight gains up to 9 kg. However, for weight gains of 9 to 14 kg, the risk of LGA for mothers with GDM was two times that for nondiabetic mothers.

In a study that defined LGA as FGR > 1.15,122 the OR for having an LGA infant given a 5 kg decrease in net gestational weight gain (total gestational weight gain minus infant birthweight) was 0.73 (95% CI, 0.68-0.79). This result is consistent with other studies reporting that the odds of LGA drops with lower gains in maternal weight.

The poor-quality studies showed similar results. LGA was significantly related to the highest weight gains among studies of GDM mothers,120 obese glucose-tolerant mothers,59 and morbidly obese mothers.54 A Finnish study68 noted that women gaining ≥ 20 kg were more likely to have babies in the higher weight gain percentile categories, but these differences were not significantly different.

Four studies stratified results by BMI status (Table 20).4,58,61,116 In a good-quality U.S. study, the estimates of LGA did not differ greatly across BMI categories.116 The ORs of LGA for rate of weight gain of 50 g per week were as follows: among underweight women, 1.25 (95% CI,

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 19. Gestational Weight Gain and LGA

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Bo et al., 2003115

Pregravid weight: Self-report

G1: OR and 95% CI, for LGA for each 1 kg increase in GWG

Italy, university clinic

700

Total weight gain: Not collected

All weights/BMI

Fair

Kitajima et al., 2001121

Pregravid weight: Self-report

G1: OR and 95% CI, for LGA for each 1 kg increase in GWG

Japan, university hospital

Total weight gain: Routine prenatal care or maternity records

146

All weights/BMI

Fair

Kramer et al., 1990122

Pregravid weight: Self-report

G1: OR and 95% CI, for LGA for each 5 kg decrease in net gestational WG

Canada, university hospital

Total weight gain: Routine prenatal care or maternity records

8,719

All weights/BMI

Fair

Muscati et al., 1996105

Pregravid weight: Medical records

G1: OR for LGA per 1 kg increase in WG up to week 20

G2: OR for LGA per 1 kg increase in WG from weeks 21 to 30

G3: OR for LGA per 1 kg increase in WG from weeks 31 to term

Canada, public health department

Total weight gain: Collected by study investigators

371

All weight/BMI

Fair

Parker and Abrams, 1992118

Pregravid weight: Self-report

ORs and 95% CIs of LGA for high WG

USA, hospital

6,690

Total weight gain: Routine prenatal care or maternity records

G1: Compared to UCSF Cohort 25-75th percentile of WG

All weights/BMI

G2: Compared to UCSF 10-90th percentile of WG

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 1.08 (1.03-1.12)

Maternal age, pregravid BMI, smoking, gestational hyperglycaemia

G1: 1.08 (0.81-1.44)

Pregravid BMI, maternal plasma glucose levels, gestational age, infant sex

G1: 0.73 (0.68-0.79)

Pregravid weight, infant sex, smoking, parity, maternal diabetes, height, previous LBW infant, severe pregnancy-induced hypertension

G1: 1.17 (P < 0.001)

G2: 1.16 (P < 0.01)

G3: 1.02 (P = NS)

Parity, pregravid standard weight, pregravid excess weight, birth length, infant sex

G1: 1.89 (1.51-2.37)

G2: 1.87 (1.39-2.52)

Maternal age, maternal race, parity, gestational age, smoking, pregravid BMI, height

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Pezzarossa et al., 1996100

Pregravid weight: Self-report

Relative risks for LGA

Italy, not stated

G1: GWG < 9 kg

G2: GWG 9-14 kg

192

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Fair

Bianco et al., 199854

Pregravid weight: Self-report

% LGA for GWG:

USA, medical center

Total weight gain: Routine prenatal care or maternity records

G1: Weight loss or 0 lbs

G2: 1-15 lbs

G3: 16-25 lbs

G4: 26-35 lbs

G5: > 35 lbs

613

Morbidly obese (BMI > 35)

Poor

Ekblad and Grenman, 199268

Pregravid weight: Medical records

Infant BW by group

Finland, hospital

Infant weight percentile for mothers with normal pregravid weight and normal weight gain

G1: < 2.5%

G2: 2.5-10%

G3: 10-50%

G4: 50-90%

G5: 90-97.5%

G6: > 97.5%

357

Total weight gain: Routine prenatal care or maternity records

Prepregnancy weight 20% over or under ideal body weight for height and normal weight

Poor

Infant weight percentile for mothers with weight gain ≤ 5 kg

G7: < 2.5%

G8: 2.5-10%

G9: 10-50%

G10: 50-90%

G11: 90-97.5%

G12: > 97.5%

Infant weight percentile for mothers with weight gain ≥ 20 kg

G13: < 2.5%

G14: 2.5-10%

G15: 10-50%

G16: 50-90%

G17: 90-97.5%

G18: > 97.5%

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: Relative risks for LGA similar between non-diabetic and GDM groups

G2: GDM group has 2 times higher risk that non-diabetics

Pregravid BMI, fasting plasma glucose

Numerical results not reported.

 

G1: 12.0

G2: 11.8

G3: 18.8

G4: 25.8

G5: 23.8

(P < 0.01)

N/A

G1: 1%

G2: 6%

G3: 35%

G4: 43%

G5: 13%

G6: 2%

N/A

G7: 3%

G8: 14%

G9: 32%

G10: 34%

G11: 14%

G12: 3%

G13: 0%

G14: 2%

G15: 42%

G16: 29%

G17: 20%

G18: 7%

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Jensen et al., 200559

Pregravid weight: Self-report

ORs and 95% CIs for LGA

Denmark, university hospitals

G1: GWG < 5.0 kg (Reference)

G2: GWG 5.0-9.9 kg

G3: GWG 10.0-14.9 kg

G4: GWG ≥ 15.0 kg

481

Total weight gain: Routine prenatal care or maternity records

Obese

Poor

Sunehag et al., 1991120

Pregravid weight: Not stated

G1: Association between LGA and GWG > 18 kg

Italy, prenatal clinics

133

Total weight gain: Not stated

All weights/BMI

Poor

BMI, body mass index; CI, confidence interval; g, grams; GDM, gestational diabetes mellitus; GWG: gestational weight gain; kg, kilogram; lbs, pounds; LGA, large-for-gestational age; N/A, not applicable; NS, non-significant; OR, odds ratio; SD: standard deviation; USCF, University of Southern California at San Francisco; WG, weight gain.

1.11-1.41); among women of normal weight, 1.14 (95% CI, 1.08-1.20); and among overweight and obese women, 1.14 (95% CI, 1.07-1.20). In a fair-quality study based on the Swedish birth registry,58 high weight gain (> 16 kg) was strongly associated with LGA, and this association was most pronounced in the lowest BMI categories. In comparison with the risk of LGA among women with weight gain between 8 and 16 kg (the reference group), adjusted ORs by BMI categories were as follows: BMI < 20, 3.26 (95% CI, 2.76-3.86); BMI ≥ 35, 1.54 (95% CI, 1.24-1.90).

In a fair-quality study of obese women,4 lower odds of LGA were observed among women who gained less than the reference group (15-25 pounds) and higher odds of LGA were observed among women who gained more the reference group. Minimal risk for LGA was observed at weight gains of 10 to 25 pounds for class I obese women (BMI 30-34.9), at gains of 0 to 9 pounds for class II obese women (BMI 35-39.9), and at gains of 0 to 9 pounds for class II obese women (BMI ≥ 40). A poor-quality study among Japanese women found that nulliparous women in the highest weight gain category (> 0.40 kg/week) had ORs for LGA of 2.25 (95% CI, 1.03-4.94) for low BMI women and 2.58 (95% CI, 1.71-3.89) for medium BMI women.61

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 1.0

G2: 2.4 (1.1-5.3)

G3: 2.1 (1.1-4.8)

G4: 4.7 (2-11)

Maternal age, pregravid BMI, gestational age, 2 hour OGTT, parity, smoking, ethnicity, clinical center

G1: χ2 = 8.2 (P < 0.005)

N/A

Eleven studies4,58,59,61,100,105,115,116,118,121,122 adjusted for potential confounders including age, pregravid BMI, glucose levels, smoking status, parity, and gestational age.


Overview of results for SGA Twenty studies examined the relationship between gestational weight gain and SGA (Evidence Table 22).4,51,54,58,59,61,66,68,89,95,105,108,111,114,116,118,119,122-124 One study was of good quality,116 twelve of fair quality,19,24,53,69,72,76,79,83,85,89-91 and seven of poor quality.11,14,20,22,29,31,59 SGA births as a percentage of all births tended to be highest for the lowest weight gains.


Detailed results for SGA As with LGA results, we discuss results relating to the simple association between weight gain and risk for SGA separately (Table 21) from those that also take BMI status into account (Table 22). Among indigent US women (fair-quality study),89 the percentage of SGA infants was 9.9 among women gaining < 0.24 kg per week, and 5.7 among the group gaining ≥ 0.75 kg per week. Similar results were observed among a cohort of Japanese women (fair-quality study),111 which defined SGA as birthweight < 1.5 SD below the mean. The percentage of SGA infants ranged from 10.9 percent in the lowest weight gain group

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 20. Gestational Weight Gain and LGA by BMI Status

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Caulfield et al., 1998116

Pregravid weight: Self-report

ORs and 95% CIs for LGA per 50g/wk increase in rate of weight gain by BMI

USA, hospital obstetric database

Total weight gain: Routine prenatal care or maternity records

G1: Underweight

G2: Normal weight

G3: Overweight

3,870

All weights/BMI

Good

Cedergren, 200658

Pregravid weight: Self-report

ORs and 95% CIs for LGA (> 2 SD above the mean)

Sweden, Medical Birth Registry

Total weight gain: Routine prenatal care or maternity records

Weight gain < 8 kg

G1: BMI < 20

G2: BMI 20-24.9

G3: BMI 25-29.9

G4: BMI 30-34.9

G5: BMI ≥ 35

245,526

All weights/BMI

Fair

Weight gain > 16 kg

G6: BMI < 20

G7: BMI 20-24.9

G8: BMI 25-29.9

G9: BMI 30-34.9

G10: BMI ≥ 35

Weight gain 8-16 kg (Reference)

Kiel et al., 20074

Pregravid weight: Medical records

G1: Odds of LGA for weight gain > 25 lbs

G2: OR of LGA for weight gain < 15 lbs

G3: Reference weight gain 15-25 lbs

USA, birth certificate registry

Total weight gain: Routine prenatal care or maternity records

120,251

Obese

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 1.25 (1.11-1.41)

G2: 1.14 (1.08-1.20)

G3: 1.13 (1.07-1.20)

Maternal age, race, parity, pregravid BMI, height, hypertension, provider type, smoking, infant sex

G1: 0.43 (0.24-0.75)

G2: 0.53 (0.47-0.61)

G3: 0.48 (0.43-0.53)

G4: 0.66 (0.59-0.75)

G5: 0.54 (0.46-0.63)

Maternal age, parity, smoking, year of birth

G6: 3.26 (2.76-3.86)

G7: 2.73 (2.60-2.88)

G8: 2.14 (2.01-2.28)

G9: 2.24 (2.00-2.51)

G10: 1.54 (1.24-1.90)

G1: Odds of LGA are higher for women in this group

G2: Odds of LGA are lower for women in this group

Maternal age, maternal race, maternal education, poverty, smoking, parity, chronic hypertension

Numerical value for ORs not reported in study

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Wataba et al., 200661

Pregravid weight: Not stated

ORs and 95% CIs for LGA

Nulliparous

G1: Low BMI (< 18), WG > 0.40 kg/wk

G2: Medium BMI (18-23.9), WG 0.20-0.25 kg/wk

G3: WG 0.25-0.30 kg/wk (Reference)

G4: Medium BMI, WG 0.30-0.35 kg/wk

G5: Medium BMI, WG 0.35-0.40 kg/wk

G6: Medium BMI, WG > 0.40 kg/wk

Japan, academic medical center

Total weight gain: Routine prenatal care or maternity records

21,718

All weights/BMI

Poor

Parous

G7: Low BMI (< 18), WG > 0.40 kg/wk

G8: WG 0.20-0.25 kg/wk (Reference for low/med BMI)

G9: Medium BMI (18-23.9), WG 0.25-0.30 kg/wk

G10: Medium BMI, WG 0.30-0.35 kg/wk

G11: Medium BMI, WG 0.35-0.40 kg/wk

G12: Medium BMI, WG > 0.40 kg/wk

G13: High BMI (≥ 24), WG 0.15-0.20 kg/wk

G14: WG ≥ 0.30 kg/wk (Reference for high BMI)

BMI, body mass index; CI, confidence interval; g, grams; g/wk, gram per week; kg/wk, kilogram per week; LGA, large-for-gestational age; OR, odds ratio; SD, standard deviation; WG, weight gain.

(< 25th percentile of weight gain) to 3.1 percent in the highest weight gain group (≥ 90th percentile of weight gain). Another fair-quality U.S. study observed an increased incidence of SGA at low weight gains; the incidence among obese women with low weight gain was two times that among obese women with normal weight gain.118 Similar results were obtained in a poor-quality study of morbidly obese women.54

Six fair-quality studies24,53,76,83,90,91 evaluated the ORs for SGA and found that the lowest weight gains (as compared to normal weight gains) were associated with ORs between 1.82 and 3.0. Among indigent U.S. women,89 the risk of SGA was highest for mothers in the lowest weight gain category (< 0.24 kg/week) when compared with women gaining 0.58 to 0.74 kg per week (OR2.24; P < 0.05). A weaker association was observed for women gaining 0.24 to 0.57 kg per week (OR1.55; P < 0.05). A U.S.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 2.25 (1.03-4.94)

G2: 1.41 (1.31-1.76)

G3: 1.0

G4: 1.76 (1.38-2.23)

G5: 2.34 (1.77-3.10)

G6: 2.58 (1.71-3.89)

G7: 2.16 (0.63-7.44)

G8: 1.0

G9: 1.48 (1.15-2.33)

G10: 1.64 (1.18-2.27)

G11: 2.23 (1.51-3.31)

G12: 3.94 (2.56-6.03)

G13: 2.27 (1.31-3.95)

G14: 1.0

Preeclampsia, C-section, 1-minute Apgar score < 4

study noted earlier also found that women with the lowest weight gains had an OR for an SGA infant of 2.06 (95% CI, 1.62-2.63) when compared with women gaining between the 25th and 75th percentile, and an OR of 1.82 (95% CI, 1.35-2.47) when compared with women gaining between the 10th and 90th percentiles.118 A U.S. study found that the OR of SGA in a second pregnancy was 1.9 (95% CI, 1.8-2.2) for weight gains less than 0.2 kg/wk as compared to weight gains greater than 0.2 kg/wk.124 The study of Japanese women noted earlier defined SGA as birthweight < 1.5 SD below the mean and gestational weight gain according to percentiles.111 Among women in the two lowest weight gain categories (very low and low) the ORs of SGA were 2.87 (95% CI, 2.56-3.21) and 1.49 (95% CI, 1.35-1.66), respectively, when compared with women in the moderate weight gain category. In addition, a significant protective effect was observed for

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 21. Gestational Weight Gain and SGA

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Parker and Abrams, 1992118

Pregravid weight: Self-report

ORs and 95% CIs of SGA for low WG

USA, hospital

Total weight gain: Routine prenatal care or maternity records

G1: Compared to UCSF Cohort 25-75th percentile of WG

G2: Compared to UCSF 10-90th percentile of WG

6,690

All weights/BMI

Fair

Cheng et al., 2004124

Pregravid weight: Self-report

OR and 95% CI, for SGA

USA, birth certificate registry

G1: WG < 0.2 kg/wk

G2: WG ≥ 0.2 kg/wk (Reference)

Total weight gain: Not stated

14,114

All weights/BMI

Fair

Cnattingius et al., 1998123

Pregravid weight: Self-report

ORs and 95% CIs for SGA

Sweden, Medical birth register

G1: WG < 0.25 kg/wk

G2:WG 0.25-0.34 kg/wk

G3: WG 0.35-0.44 kg/wk

G4: ≥ 0.45 kg/wk (Reference)

Total weight gain: Routine prenatal care or maternity records

167,750

All weights/BMI

Fair

Dawes and Grudzinskas, 1991119

Pregravid weight: Measured at first prenatal visit

Average weekly weight gain < 0.20 kg as a predictor of SGA

UK, hospital

G1: Sensitivity

G2: Specificity

Total weight gain: Routine prenatal care or maternity records

1,092

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 2.06 (1.62-2.63)

G2: 1.82 (1.35-2.47)

Maternal age, maternal race, parity, gestational age, smoking, pregravid BMI, height

G1: 1.9 (1.8-2.2)

G2: 1.0

Maternal age, education, Medicaid status, pregravid BMI, smoking, previous SGA, adequacy of prenatal care, maternal cardiac disease, preeclampsia, year of birth of second infant

G1: 3.0 (2.5-3.5)

G2: 1.9 (1.6-2.2)

G3: 1.3 (1.1-1.5)

G4: 1.0

Maternal age, parity, pregravid BMI, height, education, mother living with father, smoking

G1: 12.9%

G2: 91.3%

Maternal age, parity, pregravid BMI, weight, smoking, gestational age

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Kiel et al., 20074

Pregravid weight: Medical records

G1: Odds of SGA for weight gain > 25 lbs

G2: OR of SGA for weight gain < 15 lbs

G3: Reference Weight gain 15-25 lbs

USA, birth certificate registry

Total weight gain: Routine prenatal care or maternity records

120,251

Obese

Fair

Kramer et al., 1990122

Pregravid weight: Self-report

G1: OR and 95% CI, for SGA for each 5 kg decrease in net gestational WG

Canada, university hospital

Total weight gain: Routine prenatal care or maternity records

8,719

All weights/BMI

Fair

Muscati et al., 1996105

Pregravid weight: Medical records

G1: OR for SGA per 1 kg increase in WG up to week 20

G2: OR for SGA per 1 kg increase in WG from weeks 21 to 30

G3: OR for SGA per 1 kg increase in WG from weeks 31 to term

Canada, public health department

Total weight gain: Collected by study investigators

371

All weight/BMI

Fair

Steward and Moser, 2004114

Pregravid weight: Not stated

G1: OR and 95% CI, for SGA defined as FGR < 0.85

USA, vital statistics data

Total weight gain: Self-report

2,933

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: Odds of SGA are lower for women in this group

G2: Odds of SGA are higher for women in this group

Numerical value for ORs not reported in study

Maternal age, maternal race, maternal education, poverty, smoking, parity, chronic hypertension

G1: 1.32 (1.20-1.44)

Pregravid weight, infant sex, smoking, parity, maternal diabetes, height, previous LBW infant, severe pregnancy-induced hypertension

G1: 0.93 (P = NS)

G2: 0.85 (P < 0.01)

G3: 0.89 (P < 0.01)

Parity, pregravid standard weight, pregravid excess weight, birth length, infant sex

G1: 0.98 (0.97-0.98)

Maternal age, race, education, marital status, pregravid weight, adequacy of prenatal care, smoking, infant sex

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Takimoto et al., 2006111

Pregravid weight: Medical records

ORs and 95% CI, for SGA

Japan, obstetric units

G1: Total GWG < 25th percentile for GA

G2: Total GWG 25-49th percentile for GA

G3: Total GWG 50-74th percentile for GA (Reference)

G4: Total GWG 75-89th percentile for GA

G5: Total GWG ≥ 90th percentile for GA

Total weight gain: Routine prenatal care or maternity records

112,257

All weights/BMI

Fair

Wen et al., 199089

Pregravid weight: Measured at first prenatal visit

ORs for SGA

USA, hospital

G1: GWG < 0.24 kg/wk

G2: GWG 0.24-0.57 kg/wk

G3: GWG 0.58-0.74 kg/wk (Reference)

G4: GWG ≥ 0.75 kg/wk

Total weight gain: Routine prenatal care or maternity records

Cohort

17,149

Fair

Bianco et al., 199854

Pregravid weight: Self-report

% SGA for GWG:

USA, medical center

G1: Weight loss or 0 lbs

G2: 1-15 lbs

G3: 16-25 lbs

G4: 26-35 lbs

G5: > 35 lbs

Total weight gain: Routine prenatal care or maternity records

613

Morbidly obese (BMI > 35)

Poor

Cherry et al., 199395

Pregravid weight: Measured by study investigators

%SGA for each shifting of EW category.

USA, hospital

599

Light: < 90% EW

Normal: 90 to 110% of EW

Heavy: > 110% EW

G1: Normal to Heavy

G2: Light to Normal

G3: Heavy to Heavy

G4: Normal to Normal

G5: Light to Light

G6: Heavy to Normal

G7: Normal to Light

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 2.87 (2.56-3.21)

G2: 1.49 (1.35-1.66)

G3: 1.0

G4: 0.55 (0.55-0.72)

G5: 0.45 (0.45-0.63)

Maternal age, parity, pregravid weight, gestational age, infant sex

G1: 2.24 (P < 0.05)

G2: 1.55 (P < 0.05)

G3: 1.0

G4: 1.25 (NS)

Maternal age, race, parity, marital status, education, previous preterm delivery, alcohol use, drug use, maternal height, maternal weight, smoking, infant sex

G1: 4

G2: 3.9

G3: 5.6

G4: 3.1

G5: 3.8

N/A

G1: 22%

G2: 39%

G3: 38%

G4: 41%

G5: 62%

G6: 60%

G7: 65%

N/A

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Ekblad and Grenman, 199268

Pregravid weight: Medical records

Infant BW by group

Finland, hospital

Infant weight percentile for mothers with normal prepregnancy weight and normal weight gain

G1: < 2.5%

G2: 2.5-10%

G3: 10-50%

G4: 50-90%

G5: 90-97.5%

G6: > 97.5%

Total weight gain: Routine prenatal care or maternity records

357

Prepregnancy weight 20% over or under ideal body weight for height and normal weight

Poor

Infant weight percentile for mothers with weight gain ≤ 5 kg

G7: < 2.5%

G8: 2.5-10%

G9: 10-50%

G10: 50-90%

G11: 90-97.5%

G12: > 97.5%

Infant weight percentile for mothers with weight gain ≥ 20 kg

G13: < 2.5%

G14: 2.5-10%

G15: 10-50%

G16: 50-90%

G17: 90-97.5%

G18: > 97.5%

Jensen et al., 200559

Pregravid weight: Self-report

Rates of SGA

Denmark, university hospitals

G1: GWG < 5.0 kg (Reference)

G2: GWG 5.0-9.9 kg

G3: GWG 10.0-14.9 kg

G4: GWG ≥ 15.0 kg

Total weight gain: Routine prenatal care or maternity records

481

Obese

Poor

Lang et al., 199666

Pregravid weight: Not stated

ORs and 95% CIs for SGA

USA, hospital

G1: WG ≤ 0.40 lbs/wk

G2: WG 0.40-0.65 lbs/wk

G3: WG 0.65-0.90 lbs/wk (Reference)

G4: WG > 0.90 lbs/wk

Total weight gain: Not stated

11,505

All weights/BMI

Poor

BMI, body mass index; CI, confidence interval; EW, expected weight; FGR, fetal growth ratio; G, group; GWG, gestational weight gain; kg, kilogram; kg/wk, kilogram per week; lb, pound; NS, non-significant; OR, odds ratio; SGA, small-for-gestational age; WG, weight gain.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 1%

G2: 6%

G3: 35%

G4: 43%

G5: 13%

G6: 2%

N/A

G7: 3%

G8: 14%

G9: 32%

G10: 34%

G11: 14%

G12: 3%

 

G13: 0%

G14: 2%

G15: 42%

G16: 29%

G17: 20%

G18: 7%

 

No significant difference in rates of SGA by maternal weight gain group. Numerical results not reported in article.

Maternal age, pregravid BMI, gestational age, 2 hour OGTT, parity, smoking, ethnicity, clinical center

G1: 2.8 (2.2-3.6)

G2: 1.6 (1.4-1.9)

G3: 1.0 (Reference)

G4: 0.6 (0.5-0.7)

Maternal age, race, parity, height, pregravid weight, maternal education, health insurance, planned pregnancy, previous induced abortion, previous spontaneous abortion, previous still birth, maternal morbidity, caffeine intake, marijuana, prenatal care, smoking, infant sex

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 22. Gestational Weight Gain and SGA by BMI Status

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Caulfield et al., 1998116

Pregravid weight: Self-report

ORs and 95% CIs for SGA per 50g/wk increase in rate of weight gain by BMI

USA, hospital obstetric database

Total weight gain: Routine prenatal care or maternity records

3,870

G1: Underweight

G2: Normal weight

G3: Overweight

All weights/BMI

Good

Cedergren, 200658

Pregravid weight: Self-report

ORs and 95% CIs for SGA (< 2 SD below the mean)

Sweden, Medical Birth Registry

Total weight gain: Routine prenatal care or maternity records

Weight gain < 8 kg

G1: BMI < 20

G2: BMI 20-24.9

G3: BMI 25-29.9

G4: BMI 30-34.9

G5: BMI ≥ 35

245,526

All weights/BMI

Fair

Weight gain > 16 kg

G6: BMI < 20

G7: BMI 20-24.9

G8: BMI 25-29.9

G9: BMI 30-34.9

G10: BMI ≥ 35

Weight gain 8-16 kg (Reference)

Cheng et al., 2004124

Pregravid weight: Self-report

95% CIs of SGA for low weight gain (< 0.2 kg/wk) by BMI

USA, birth certificate registry

Total weight gain: Not stated

14,114

G1: Underweight

G2: Normal weight

G3: Overweight

G4: Obese

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 0.87 (0.78-0.97)

G2: 0.90 (0.84-0.96)

G3: 0.93 (0.86-1.01)

Maternal age, race, parity, pregravid BMI, height, hypertension, provider type, smoking, infant sex

G1: 2.35 (1.92-2.88)

G2: 1.99 (1.77-2.23)

G3: 1.75 (1.48-2.07)

G4: 1.68 (1.26-2.25)

G5: 1.71 (1.03-2.85)

Maternal age, parity, smoking, year of birth

G6: 0.50 (0.41-0.61)

G7: 0.50 (0.45-0.56)

G8: 0.57 (0.47-0.68)

G9: 0.61 (0.40-0.93)

G10: 0.50 (0.20-1.24)

G1: (1.2-2.4)

G2: (1.9-2.7)

G3: (1.6-2.9)

G4: (1.4-2.1)

Maternal age, education, Medicaid status, pregravid BMI, smoking, previous SGA, adequacy of prenatal care, maternal cardiac disease, preeclampsia, year of birth of second infant

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Zhou and Olsen, 1997108

Pregravid weight: Self-report

% Growth retardation (birthweight < 3,000g and placental weight > 490g) by weight gain category and BMI

Denmark, two communities

Total weight gain: Routine prenatal care or maternity records

Cohort

7,122

Weight gain < 11 kg

G1: Underweight (Reference)

G2: Normal

G3: Overweight

Fair

Weight gain 12-15 kg

G4: Underweight

G5: Normal

G6: Overweight

Weight gain > 16 kg

G7: Underweight

G8: Normal

G9: Overweight

Kabiru and Raynor, 200451

Pregravid weight: Measured at first prenatal visit

% SGA

G1: No change in BMI category

G2: 1 category increase in BMI

G3: > 1 category increase in BMI

USA, hospital

5,131

Total weight gain: Routine prenatal care or maternity records

All weights/BMI

Poor

% SGA among overweight G4: No change in BMI category

G5: 1 category increase in BMI

G6: > 1 category increase in BMI

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 1.0

G2: 0.6 (0.4-0.8)

G3: 0.6 (0.4-1.1)

Maternal age, parity, alcohol, diabetes, term delivery, smoking, gestational age, infant sex

G4: 0.3 (0.2-0.5)

G5: 0.4 (0.3-0.6)

G6: 0.4 (0.1-1.0)

G7: 0.3 (0.2-0.5)

G8: 0.2 (0.1-0.3)

G9: 0.2 (0.1-0.6)

G1: 19.5%

G2: 13.5%

G3: 9.5%

G4: 14.2%

G5: 9.9%

G6: 11.5%

N/A

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Wataba et al., 200661

Pregravid weight: Not stated

ORs and 95% CIs for SGA

Japan, academic medical center

Parous, Low BMI (< 18)

G1: WG < 0.15 kg/wk

G2: WG 0.15-0.20 kg/wk

G3: WG 0.20-0.25 kg/wk

G4: WG 0.25-0.30 kg/wk (Reference

Total weight gain: Routine prenatal care or maternity records

21,718

All weights/BMI

Poor

Parous, Medium BMI (18-23.9)

G5: WG < 0.15 kg/wk

G6: WG 0.15-0.20 kg/wk

G7: WG 0.20-0.25 kg/wk (Reference)

Parous, High BMI (> 24)

G8: WG < 0.15 kg/wk

G9: WG 0.15-0.20 kg/wk (Reference)

Nulliparous, Low BMI (< 18)

G10: WG < 0.15 kg/wk

G11: WG 0.15-0.20 kg/wk

G12: WG 0.20-0.25 kg/wk

G13: WG 0.25-0.30 kg/wk (Reference

Nulliparous, Medium BMI (18-23.9)

G14: WG < 0.15 kg/wk

G15: WG 0.15-0.20 kg/wk

G16: WG 0.20-0.25 kg/wk

G17: WG 0.25-0.30 (Reference)

Nulliparous, High BMI (> 24)

G18: WG < 0.05 kg/wk

G19: WG 0.15-0.20 kg/wk (Reference)

BMI, body mass index; cat, category; CI, confidence interval; g, gram; G, group; kg, kilogram; kg/wk, kilogram per week; lbs, pounds; med, medium; OR, odds ratio; SD, standard deviation; SGA, small-for-gestational age.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: 5.42 (2.86-10.27)

G2: 2.78 (1.53-5.06)

G3: 1.39 (0.82-2.42)

G4: 1.0

Preeclampsia, C-section, 1-minute Apgar score < 4

G5: 2.21 (1.67-2.93)

G6: 1.68 (1.23-2.07)

G7: 1.0

G8: 2.82 (1.17-6.78)

G9: 1.0

G10: 6.20 (2.72-14.09)

G11: 2.58 (1.14-5.87)

G12: 2.46 (1.19-5.08)

G13: 1.0

G14: 2.64 (1.88-3.71)

G15: 1.60 (1.15-2.23)

G16: 1.39 (1.03-1.87)

G17: 1.0

G18: 7.06 (2.11-23.61)

G19: 1.0

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

the two highest weight gain categories. One study, using data from the Swedish Medical Birth Registry, observed higher rates of SGA (here defined as < 2 SD below the mean) among the lowest weight gain groups.123 Specifically, women gaining < 0.25 kg per week had an OR of 3.0 (95% CI, 2.5-3.5) when compared with women gaining ≥ 0.45 kg per week. The ORs decreased as gestational weight gain category dropped. Similar results were found in a study of obese women.4

Among white nonsmokers in Canada (fair-quality study),105 for each 1 kg increase in weight gain up to week 20, the OR of an SGA infant was 0.93 (not significant); for weight gain from weeks 21 to 30, it was 0.85 (P < 0.01); and for weight gain from week 31 to term, it was 0.89 (P < 0.01). In other words, increases in weight gain from weeks 21 to term lowered a woman’s risk of an SGA infant. A fair-quality study of the predictors of SGA found that average weekly weight gain < 0.20 kg had 12.9 percent sensitivity and 91.3 percent specificity.119

Two fair-quality studies defined growth restriction using FGR, with SGA specified as an FGR < 0.85.79,89 In general, increases in weight gain were associated with lower risks of SGA. Specifically, one study found an OR of 0.98 (95% CI, 0.97-0.98) for each 1 kg increase in total gestational weight gain.114 Another study found an OR of 1.32 (95% CI, 1.20-1.44) for each 5 kg decrease in net gestational weight gain (total gestational weight gain minus infant birthweight).122

In a poor U.S. study,66 using women gaining 0.65 to 0.9 pounds per week as the reference group, women gaining ≤ 0.40 pounds per week had an OR for an SGA infant of 2.8 (95% CI, 2.2-3.6), and women gaining 0.4 to 0.65 pounds per week an OR of 1.6 (95% CI, 1.4-1.9). In this study, however, women gaining > 0.9 pounds per week also experienced a significant protective effect against SGA (OR, 0.6; 95% CI, 0.5-0.7).

The results from three14,20,31 poor-quality studies did not find statistically significant results. One study was among Finnish women,68 one defined SGA as birthweight < 2 SD below the mean,59 and one study was among morbidly obese women.54 A study among adolescents (also rated poor) looked at the proportion of infants who gained less than the median weight (instead of the 10th percentile).95 Mothers who shifted to higher weight classes had fewer infants who fell below the median for intrauterine growth; women who did not maintain their weight and shifted to lower weight classes were more likely to have infants below the median for intrauterine growth.

Six studies presented stratified analyses by BMI (Table 22).11,19,22,72,81,91 In general, the risk of SGA among women with low weight gain decreased as BMI increased.

A U.S. database study (rated good quality) found that increasing rates of weight gain were associated with reduced risk of an SGA infant, with

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

the risk decreasing with increasing BMI.116 Specifically, the ORs of SGA for each 50 g per week increase in maternal weight were as follows: 0.87 (95% CI, 0.78-0.97) for underweight mothers; 0.90 (95% CI, 0.84-0.96) for mothers of normal weight; and 0.93 (95% CI, 0.86-1.01) for overweight and obese women. In the Swedish birth registry study (rated fair quality), the risk of SGA was higher in the low weight gain group (< 8 kg), but the risk decreased with increasing BMI.58 Using women gaining between 8 and 16 kg as the reference group, these researchers reported that the OR for delivering an SGA infant for women with low weight gain (< 8 kg) was 1.71 (95% CI, 1.03-2.85) among women with a BMI ≥ 35; it was 2.35 (95% CI, 1.92-2.88) among women with a BMI < 20. Women gaining > 16 kg were at decreased risk for delivering an SGA infant, with the risk being similar between all BMI categories.

Among nondiabetic women in Denmark (fair-quality study) for whom SGA was defined as birthweight < 3,000 g despite placenta weight being above the 66th percentile (491 g), women who gained more than 16 kg were at lower risk of delivering an SGA infant; this risk was the same regardless of BMI status.108 The risk of SGA decreased with increasing weight gain, and it also tended to decrease as BMI increased. In a U.S. study, 95% CIs of the OR of SGA for low weight gain (< 0.2 kg/wk) compared to weight gain > 0.2 kg/wk, were similar across BMI categories: underweight (95% CI, 1.2-2.4), normal weight (95% CI, 1.9-2.7), overweight (95% CI, 1.6-2.9), obese (95% CI, 1.4-2.1).124

A poor-quality study of the effect of changing BMI categories found that excessive weight gain (defined in various ways depending on BMI) was associated with lower rates of SGA for two groups of women: normal weight (excessive gain, > 35 pounds; P = 0.016) and overweight (excessive gain, > 25 pounds; P = 0.003); this association did not hold for obese women.51 A study among Japanese women (also poor quality) found high risks for SGA among nulliparous women with low BMI (< 18) and low rates of weight gain (< 0.15 kg/week).61

Sixteen of these studies adjusted for multiple confounding factors such as age, pregravid BMI, smoking, glucose levels, parity, race, gestational age, marital status, height, education, and sex of infant.19,20,22,24,29,53,69,72,76,79,81,83,85,89-91

Apgar scores

Study characteristics Four studies, set in Sweden,58 the United States,33,92 and Japan,61 examined the effect of gestational weight gain on Apgar scores (Evidence Table 23, Table 23). Apgar scores, calculated on the basis of five criteria (appearance, pulse, grimace, activity, respiration), range from 0 to 10. Three were cohort studies; the fourth was a case-control study

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 23. Gestational Weight Gain and Apgar Scores

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Cedergren, 200658

Pregravid weight: Self report, if unknown, standardized measurement is made during first visit to maternity health care center

Weight gain < 8 kg, 8-16 kg, and > 16 kg for each BMI class below

Sweden, Medical Birth Registry

G1: BMI < 20

G2: BMI 20-24.9

G3: BMI 25-29.9

G4: BMI 30-34.9

G5: BMI ≥ 35

245,526

All weights/BMI

Total weight gain: Measured when woman entered delivery unit

Fair

Johnson et al., 199270

Pregravid weight: Self report collected at first antepartal visit

G1: total weight gain < 16 lb

G2: total weight gain 16-25 lb

G3: total weight gain 26-35 lb

G4: total weight gain > 35 lb

USA, prenatal clinics

3,191

Total weight gain: Last prenatal visit

All weights/BMI

Fair

Nixon et al., 1998125

Pregravid weight: Routine data forms, self report collected at first prenatal visit

Continuous weight gain measure

USA, county nurse-midwifery services

Total weight gain: Routine data forms, prenatal care or maternity records prior to delivery

2,228

All weights (IOM)

Fair

Wataba et al., 200661

Pregravid weight: Hospital database/register

Rate of weight gain, categorized differently across different BMI groups

Japan, academic medical center

Total weight gain: Hospital database/record

21,718

All weights/BMI

Poor

AOR, adjusted odds ratio; BMI, body mass index; kg/wk, kilogram per week.

examining outcomes of macrosomic infants (≥ 4,000 g) and normal-weight babies (2,500-3,999 g).125


Overview of results These four studies, three rated fair19,33,92 and one poor,61 did not provide consistent evidence on the direction or trend of effect. These studies inconsistently controlled for confounders. None

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

No association between low weight gain and Apgar score (< 7), despite BMI of mother

BMI, maternal age, parity, smoking in early pregnancy, year of birth

Increased OR for gestational weight gain on 1-minute and 5-minute Apgar score ≤ 7, persists after adjusting (no further details provided)

Prepregnancy weight quartile, height (tertile), BMI category, race, parity, hypertension, other variables entered by stepwise regression model

Gestational weight gain was not a predictor of Apgar scores < 7

Age, parity, BMI

AOR for 1 min Apgar scores < 4 for nulliparous women with low BMI, weekly weight gain < 15 kg/wk, compared with women gaining 0.25-0.3 kg/wk: 12.24 (2.04-73.43)

Parity, baseline BMI

AOR for 1 min Apgar scores < 4 for parous women with medium BMI, weekly weight gain 0.35-0.4 kg/wk compared with women gaining 0.2-0.25 kg/wk: 2.21 (1.08-4.53)

No other relationships were significant

controlled for a range of maternal pregnancy complications that could account for low Apgar scores.


Detailed results Three studies examined 1-minute or 5-minute Apgar scores at two levels: > 7 or ≥ 7. Two found no association between gestational weight gain and Apgar scores.19,92 The third found increased ORs for

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

gestational weight gain, after adjusting for prepregnancy weight quartile, height (tertile), BMI category, race, parity, hypertension, and other variables entered by stepwise regression model, but the authors provided no further details on the magnitude of the effect.70

One poor-quality study examined associations between 1-minute Apgar scores > 4 and rates of weekly weight gain (7 categories), categorized differently across different BMI groups (3 groups) and parity (2 categories), resulting in 42 comparisons.61 Two comparisons were statistically significant: (1) higher risk for low Apgar scores for nulliparous women with low BMI and lower-than-median weight gain for their peer group; and (2) higher risk for parous women with medium BMI with higher-than-median weight gain for their peer group.

Infant Outcomes
Perinatal mortality

Study characteristics Three studies, two set in the United States93,94 and one in Denmark,126 looked at the association between maternal weight gain and mortality, defined in one study as stillbirth126 and in two others as perinatal mortality (neonatal plus fetal deaths)93,94 (Table 24, Evidence Table 24). All three studies used different definitions of maternal weight gain:

  • weight gain per week;126

  • optimal weight gain127 defined as 36 to 40 pounds for underweight women, 31 to 40 pounds for women of ideal prepregnancy weight, and 26 to 30 pounds for overweight women, based on associations between maternal prepregnancy weight, height, weight gain, and adverse perinatal outcomes; and

  • low weight gain (< 0.8 kg per week).128

Overview of results One of these studies was rated poor quality128 and the others were rated fair. These studies suggest a protective effect of gestational weight gain on perinatal mortality but not on stillbirth.


Results for categorical measures of weight gain Both studies that focused on optimal or low weight gain found a protective effect of weight gain on infant mortality, but variations in the definition of maternal weight gain and the outcome do not allow quantification of the magnitude of the effect.93,94


Results for rate of weight gain The study that examined associations between weight gained per week and stillbirth found no effect of weight

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 24. Gestational Weight Gain and Perinatal Mortality

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Bracero and Byrne, 1997127

Pregravid weight: Self-report at first prenatal visit

G1: Suboptimal weight gain

G2: Optimal weight gain

Perinatal mortality%

G1: 0.6

G2: 0.2

P < 0.0001

NA

USA, hospital

Total weight gain: Last prenatal assessment

20,971

All

weights/BMI

Fair

Nohr et al., 2005126

Pregravid weight: Self-report of pre-pregnancy weight at first telephone interview between 9 and 24 weeks weeks

Weight per week for BMI groups (underweight < 18.5; 18.5 ≤ normal weight < 25; 25 ≤ overweight < 30; and obese ≥ 30)

Weight gain in pregnancy was not significantly associated with the risk of stillbirth for any BMI groups.

AOR adjusted for age, height, parity, sociooccupational status, physical exercise, smoking, alcohol and coffee consumption

Denmark, National Birth Cohort

Total weight gain:

Average weekly increase between self reported weights in first and second pregnancy interviews for women who provided a first interview between 9-24 weeks, those who provided a second interview between 26 and 38 completed weeks of gestation, and those who had at least 6 weeks between 2 interviews

54,505

All weights/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Date Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Naeye, 1990128

Pregravid weight: Self-report at first antenatal care visit

Low weight gain defined as < 0.8 kg/week after the first trimester for pregravid BMI groups below:

G1: BMI < 20

G2: BMI 20-24

G3: BMI 25-30

G4: BMI > 30

Attributable risk estimates for perinatal death for low pregnancy weight gain

G1: 0.03

(95% CI, 0.02-0.05)

G2: 0.02

(95% CI, 0.01-0.03)

G3: 0.01

(95% CI, 0.00-0.02)

G4: 0.00

Age 35-40, diabetes mellitus, hypertensive disorders, black, preterm birth, major congenital malformations, twins, neonatal respiratory distress syndrome

USA, hospitals affiliated with medical schools

Total weight gain: Data from medical records after first trimester

56,857

All weights/BMI

Poor

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

gain on stillbirth within groups defined by BMI.126 It found increased risks of stillbirth with pregravid obesity and overweight status. This association between higher pregravid weight and stillbirth persisted after the investigators excluded women with obesity-related diseases (diabetes, preeclampsia, and other hypertensive disorders). Within this subset of women without obesity-related diseases (n = 39,187), the AOR for stillbirth related to an increased weight of 100 g per week was 0.94 (95% CI, 0.87-1.03).

Neonatal distress

Study characteristics A Swedish study examined the effects of gestational weight gain on fetal distress (equivalent to International Classification of Diseases [ICD] 9-codes 768.2-4; and ICD 10-codes P20.0, P20.1, and P20.9) using medical birth registry data from 245,526 singleton, term pregnancies over a 9-year period. (Evidence Table 25).58 Women were grouped by BMI status into three gestational weight gain categories: < 8 kg (low), 8 to 16 kg, and > 16 kg (high).


Overview of results The results of this fair study show that after adjusting for maternal age, parity, smoking in early pregnancy, and year of birth, the authors reported that fetal distress was not significantly associated with low weight gain despite the BMI of the mother. Overweight and morbidly obese women with excessive weight gain did have an increased risk for fetal distress.


Detailed results Compared with women with gestational weight gain of 8-16 kg, the OR for fetal distress among women gaining 16 kg or more was 2.15 (95% CI, 1.10-4.20) for women with BMI ≥ 35 and 1.31 (95% CI, 1.05-1.53) for women with BMI 25-29.9.

Neonatal hypoglycemia

Study characteristics Two studies examined the effect of gestational weight gain on neonatal hypoglycemia (Evidence Table 26).75,96 One was a retrospective cohort study of 20,465 women;129 the other110 was a retrospective case-control study using data from 45,245 singleton, live births from a US prepaid group practice health plan. The studies categorized gestational weight gain differently; one examined gestational weight gain as a dichotomous variable based on extremes of weight gain (< 7 kg and > 18 kg),129 and the other used maternal rate of weight gain (total pregnancy weight gain minus infant birthweight divided by weeks of gestation when the last weight was measured) in kg per week.110 Hypoglycemia was defined by ICD codes129 or as at least one plasma glucose test result < 40 mg/dL.110

In the case-control study,110 babies were identified as cases if they had

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

the following complications: macrosomia (birthweight > 4,500 g), hypoglycemia (at least one plasma glucose < 40 mg/dL), or hyperbilirubinemia (at least one total serum bilirubin of 20 mg/dL or more). In general, hypoglycemic cases tended to be infants whose mothers were younger, nonwhite, and less educated than mothers of controls. More women with a prepregnancy BMI > 29.0 appeared among the cases (22.9 percent) than the controls (17.6 percent).


Overview of results The results of these studies (1 good110 and 1 fair129) suggest that gestational weight gain is associated with the risk of infant hypoglycemia.


Results In the case-control study (rated good quality),110 after adjusting for age, race-ethnicity, parity, plasma screening value, and gestational age at last weight measured, the authors found that women who gained in the highest bracket of weight gain per week (more than 0.40 kg/week) had a increased risk of delivering an infant with hypoglycemia (AOR, 1.94; 95% CI, 1.33-2.82) than women gaining 0.22 to 0.31 kg per week.

Findings from the retrospective cohort study were similar.129 After controlling for several confounders, the authors found that weight gain of more than 18 kg was associated with hypoglycemia (AOR, 1.67; 95% CI, 1.13-2.46) when compared with weight gain of 11.5 to 16.0 kg.

Hyperbilirubinemia

Study characteristics The retrospective case-control study described above also examined the effect of gestational weight gain on infant hyperbilirubinemia (Evidence Table 27).110


Overview of results One good study110 suggested that increased gestational weight gain is associated with a higher risk of hyperbilirubinemia.


Detailed results Compared with controls, the hyperbilirubinemia case group had more Asians (20.1 percent vs. 8.1 percent) and tended to be born at a gestational age < 37 weeks. Compared with women gaining 0.22 to 0.31 kg per week, women who gained in the highest bracket of weight gain/week (more than 0.40 kg/week) had an increased risk of delivering an infant with hyperbilirubinemia (AOR, 1.94; 95% CI, 1.33-2.82).

Neonatal hospitalization

Study characteristics One study investigated the influence of gestational weight gain on perinatal outcomes, including hospitalization of infant (Evidence Table 28).12 Using a hospital-based, retrospective cohort study design, the authors studied 633 women who delivered live, singleton babies in Japan between 24 and 42 weeks’ gestation. Mean age of the

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

women was 29.1 and most were nulliparas. Most of the women gained between 8.5 and 12.5 kg (mean, 10.5 kg) during their pregnancy. Gestational weight gain was collected from maternity records and was based on last weight taken at the hospital prior to delivery.


Overview of results One fair study suggested that infants of women who gained less than 8.5 kg during their pregnancy were 60 percent more likely to require hospitalization.12


Detailed results Overall, 13.3 percent had babies with complications requiring hospitalization, excluding admissions for phototherapy necessitated by neonatal jaundice. After adjusting for maternal age, parity, smoking, prepregnancy BMI, and gestational age, the authors did not find a significant relationship between gestational weight gain of less than 8.5 kg (AOR, 1.60; 95% CI, 0.88-2.88) or weight gain greater than 12.5 kg (AOR, 0.93; 95% CI, 0.46-1.88) and hospitalization of infant.

Other infant morbidity

Study characteristics Two studies addressed other neonatal morbidity in association with gestational weight gain (Evidence Table 29); one was the large cohort study noted above,129 and the other used a case-control design.130 Both studies relied on self-reported prepregnancy weights. Total weight gained during pregnancy was ascertained from prenatal records129 and women’s self-report.130 The studies differed on how gestational weight gain was categorized: the cohort study categorized gestational weight gain according to both the IOM recommendations (i.e., the woman was below, within, or above the IOM thresholds) and by extremes of weight gain (< 7 kg, > 15 kg); the case-control study defined gestational weight gain as a continuous variable.


Overview of results One fair study reported that gestational weight gain less than 7 kg was associated with neonatal seizure.129 Another fair study reported no significant association between infant leukemia and weight gain during pregnancy.130


Detailed results The cohort study looked at the relationship between gestational weight gain and several adverse neonatal outcomes (birth trauma, 5-minute Apgar score < 7, need for assisted ventilation, SGA, LGA, umbilical cord arterial pH < 7.1, umbilical cord arterial base excess < 10, admission to the neonatal intensive care unit [NICU], admission to the special-care nursery [a step-down unit], neonatal infection, seizure, hypoglycemia, polycythemia, jaundice, meconium aspiration syndrome, respiratory distress or tachypnea, anemia, birth asphyxia, and perinatal death).129 The authors controlled for maternal age, race, parity, smoking, pregravid

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

BMI, date of delivery, pregnancy-induced hypertension, mode of delivery, length of first stage of labor, length of second stage of labor, gestational age, and birthweight. Using weight gain of 11.5 to 16 kg as a reference, the authors reported that gestational weight gain less than 7 kg was associated with neonatal seizure (AOR, 10.66; 95% CI, 2.17-52.36). Gestational weight gain > 18 kg was associated with assisted ventilation (AOR, 1.52; 95% CI, 1.16-2.00), seizure (AOR, 6.19; 95% CI, 1.32-28.96), polycythemia (AOR, 1.59; 95% CI, 1.13-2.22), and meconium aspiration syndrome (AOR, 1.86; 95% CI, 1.13-3.05).

The case-control study130 examined the association between maternal reproductive history, including gestational weight gain, and the risk of infant leukemia in 240 cases, defined as infant leukemia diagnosed at < 1 year of age, and 255 controls matched to cases by year of birth. Infants with infant leukemia were significantly (P < 0.003) less likely to be white (79.5 percent vs. 85.5 percent) and more likely to be Hispanic (10.5 percent vs. 3.5 percent) than controls. After adjusting for sex, race or ethnicity, maternal education, and prepregnancy BMI, the authors found no significant association between infant leukemia and weight gain during pregnancy.

Infant BMI

Study characteristics Two older studies examined the influence of gestational weight gain on the offspring’s BMI (Evidence Table 30). One cohort study comprised 8,719 singleton, live-born infants from a hospital in Montreal, Canada, from 1980 to 1986.122 Of these mothers, 48 percent were primiparas, 90 percent were married, and 87 percent had started prenatal care in the first trimester. The infant’s weight and length at birth was used to calculate BMI. Weight gain was expressed as total weight gain minus the weight of the infant at birth. The second study enrolled 119 term GDM and 143 term control mother-infant dyads from a hospital in Rhode Island in 1982.131 The mothers were all screened for gestational diabetes using a universal screen approach between 24 and 28 weeks’ gestation. Anthropometric measurements on the infants were done by study staff on the second day of life; weight and height was used to calculate infants’ BMI. Total gestational weight gain was defined as measured weight at last prenatal visit (within one week of delivery) minus self-reported pregravid weight.


Results The Canadian study reported that net gestational weight gain was weakly but significantly correlated with infant’s BMI (r = .04, P < 0.01).122 In multivariate analysis, net gestational weight gain did not meet the criterion threshold for remaining in the stepwise regression.122

In the U.S. study, total gestational weight gain was significantly correlated with infant’s BMI (r = .22, P = 0.01).131 In multivariable regression

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

analysis done separately for mothers with GDM and controls, total gestational weight gain significantly predicted infant’s BMI such that a 1 kg increase in weight gain was associated with a 0.06 and 0.05 increase in BMI for GDM and control infants, respectively, after controlling for pregravid BMI and glucose values. The difference between the results of these two studies lies in the fact that once the weight of the infant is removed from total weight gain, an important product of conception is missing from the measure of weight gain and thus the strength of the association is reduced.131

Other infant growth characteristics

Study characteristics Six studies examined the association between gestational weight gain and various other infant growth characteristics (Evidence Table 31, Table 25).31,56,57,62,82,89


Overview of results The evidence from one good,98 three fair,14,56,57,82 and one poor study68 suggest that gestational weight gain is associated with various measures of infant growth characteristics. A single fair study failed to find an association between gestational weight gain and infant proportionality.122


Detailed results One good-quality study analyzed the relationship between weight gain (total and by trimester) and ponderal index (PI, a way of characterizing the relationship of height to mass for an individual).98 Each kilogram of weight gained in the first and third trimesters significantly increased the PI: first trimester, an estimated 0.21 units; third trimester, by 0.12 units. Second trimester weight gain was not associated with newborn PI. The authors adjusted their models for gestational age, sex, parity, maternal height, maternal age, and pregravid BMI.

A retrospective cohort study (rated fair quality) conducted in France examined predictors of various infant growth measures,92 using standardized coefficients (SC) from stepwise regression models. SCs are regression coefficients calculated as if all of the independent variables had a variance of 1. Pregnancy weight gain had a significant influence on birthweight (SC 0.199), crown-heel length (SC 0.142), head circumference (SC 0.120), and subscapular skinfold thickness (SC 0.146).

One fair-quality study examined proportional weight gain in relation to fetal growth rate in millimeters (mm) per day, calculated by averaging three ultrasound measurements of the sagital and transverse diameters of the fetal abdomen in three study time periods.117 Increases in proportional weight gain during the second period (weeks 25 to 33) and third period (weeks 33 to 37), but not the first period (weeks 17 to 25) were significantly associated with significant increases in fetal growth. These results were adjusted for age, BMI, smoking, history of delivering an SGA infant, and infant sex.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 25. Gestational Weight Gain and Other Infant Growth Measures

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Brown et al., 200298

Pregravid weight: Measured by study investigators

G1: Increase in ponderal index per 1 kg increase in first trimester weight gain

G2: Increase in ponderal index per 1 kg increase in second trimester weight gain

G3: Increase in Ponderal Index per 1 kg increase in third trimester weight gain

USA, primary care clinics

Total weight gain: Collected by study investigators

389

All weight/BMI

Good

Guihard-Costa et al., 200492

Pregravid weight: Routine prenatal care

G1: SC for effect of GWG on crown-heel length

G2: SC for effect of GWG on head circumference

G3: SC for effect of GWG on subscapular skinfold thickness

France, hospital database

Total weight gain: Routine prenatal care or maternity records

13,972

All weights/BMI

SCs are regression coefficients calculated as if all of the independent variables had a variance of 1

Fair

Kirchengast and Hartmann, 200393

Pregravid weight: Estimated from measured weight at first prenatal visit

Change in infant size characteristics per 1 kg increase in GWG

Austria, university hospital

G1: Birth length (cm)

G2: Head circumference (cm)

G3: Acromial circumference (cm)

G4: Diameter frontoccipitalis (cm)

Total weight gain: Routine prenatal care or maternity records

8,011

All weights/BMI

Fair

Kramer et al., 1990122

Pregravid weight: Self-report

Correlation coefficients between GWG and:

Canada, university hospital

G1: Length

G2: Head circumference

G3: BMI

G4: Ponderal Index

G5: Weight/Head circumference

Total weight gain: Routine prenatal care or maternity records

8,719

All weights/BMI

Net gestational weight gain was associated with correlation coefficients of −0.04 for length, −0.01 for head circumference, 0.04 for BMI, 0.04 for Ponderal Index, and 0.01 for weight/head circumference. Results were significant

(P < 0.01) for length, BMI, and Ponderal Index

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: β = 0.21 (P < 0.0003)

Maternal age, parity, pregravid BMI, height, infant sex, gestational age

G2: β = 0.05 PI (P < 0.4)

G3: β = 0.12 (P < 0.03)

G1: SC 0.142

G2: SC 0.120

G3: SC 0.146

Maternal age, parity, pregravid BMI, height

G1: β = 0.55 (0.43-0.68)

G2: β = 0.33 (0.23-0.42)

G3: β = 0.47 (0.39-0.55)

G4: β = 0.12 (0.07-0.18)

Maternal age, age at menarche, pregravid weight, height, distantia cristarum

G1: −0.04 (P < 0.01)

G2: −0.01

G3: 0.04 (P < 0.01)

G4: 0.04 (P < 0.01)

G5: 0.01

Pregravid weight, infant sex, smoking, parity, maternal diabetes, height, previous LBW infant, severe pregnancy-induced hypertension

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Shepard et al., 1996117

Pregravid weight: Medical records

Increase in mean abdominal fetal growth rate (mm/day) per 5% increase in proportional weight gain in this period:

Norway and Sweden, multicenter study

Total weight gain: Measured at 3 study time periods

G1: Weeks 17-25

G2: Weeks 25-33

G3: Weeks 33-37

369

All weights/BMI

Fair

Ekblad and Grenman, 199268

Pregravid weight: Medical records

Mean symphysis-fundus height:

G1: Weight gain ≤ 5 kg

G2: Weight gain 5-20 kg

G3: Weight gain ≥ 20 kg

Finland, hospital

Total weight gain: Routine prenatal care or maternity records

357

Prepregnancy weight 20% over or under ideal body weight for height and normal weight

Poor

β, unstandardized coefficient from multiple regression; BMI, body mass index; cm, centimeters; g, gram; GWG, gestational weight gain; kg, kilogram; SC, standardized coefficient; SGA, small-for-gestational age.

Infant body proportionality was studied in a Canadian population (rated fair quality) with validated gestational ages.122 Proportionality was evaluated using z transformations of crown-heel length, head circumference, BMI, PI, and birthweight/head circumference. Net gestational weight gain was associated with correlation coefficients of −0.04 for length, 0.04 for BMI, and 0.04 for PI (all P < 0.01). ORs of low and high PI for each 5 kg decrease in net gestational weight gain were not significant.

A fair-quality study conducted in Austria found that for each 1 kg increase in total gestational weight gain, birth length increased by 0.55 cm (95% CI, 0.43-0.68), head circumference increased by 0.33 cm (95% CI, 0.23-0.42), acromial circumference increased by 0.47 cm (95% CI, 0.39-0.55), and diameter frontoccipitalis increased by 0.12 cm (95% CI, 0.07-0.18).93 This study adjusted for maternal age, age at menarche, pregravid weight, height, and distantia cristarum.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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Results

Confounders and Effect Modifiers Included in Analysis

G1: β = 0.35 (P = 0.49)

G2: β = 0.88 (P = 0.02)

G3: β = 1.53 (P = 0.02)

Maternal age, pregravid BMI, previous SGA, infant sex

G1: 30.8 cm ± 4.0

G2: 32.8 cm ± 3.4

G3: 35.0 cm ± 3.9

N/A

Finally, a poor-quality retrospective cohort study conducted in Finland examined the relationship between weight gain and symphysis-fundus (SF) height.68 SF height did not differ significantly between weight gain groups at 24 weeks, but higher gestational weight gains were associated with longer SF height.

Child Outcomes
Childhood weight status

Study characteristics Four studies, using different definitions of outcomes, examined the long-term effect of gestational weight gain on children’s weight status (Evidence Table 32).99-102 Three studies enrolled the subjects at birth and then followed them through various end points; up to

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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15 months postpartum,132 3 years of age,24 and 2 and 5 years for the Avon longitudinal study of pregnancy and childhood (ALSPAC) in England.133 All three included only singleton births. One was conducted using a national representative sample from 1979 that followed the children of mothers who were born in 1984, 1986, 1988, and 1990 for up to 12 years.134


Overview of results Due to the different definitions of the outcomes, the results from three fair100-102 and one poor99,102 studies are mixed for an association between gestational weight gain and childhood weight status.


Detailed results In the ALSPAC study (rated fair), which used as its outcome “catch up growth” from birth to 2 years of age (for definition see Table 26), bivariate analysis suggested that children who showed catch-up growth were no different in the amount of weight that their mothers gained during pregnancy than children who showed no change or those who had catch-down growth. No adjustments were made for confounding.

In another fair study that reported on the effect of total weight gain and net weight gain (excluding infant birthweight),24 child BMI percentiles at age 3 were grouped as follows: below 50th (referent category), 50th to 84th, 85th to 94th, and 95th or higher. Gestational weight gain was associated with a BMI of ≥ 95 percentile in both bivariate and multivariate analysis; a 5 kg increase in weight gain was associated with a 52 percent increase in risk of obesity in the offspring. Gestational weight gain was also associated with BMI z score. Similar associations were found when using net weight gain as the exposure.

The one poor study that examined BMI ≥ 85th percentile at ages less than 14 months did not find any association with gestational weight gain.132 However, the nationally representative study did find an association for early onset of overweight associated with weight gains ≥ 20.43 kg (≥ 45 lbs) but not later on in life.134

The U.S. study (rated poor quality) determined, using multivariable logistic regression models, that gestational weight gain was a significant predictor of infant obesity at 1 and 14 months of age.132 The odds of obesity rose 10 percent at 1 month for every 5-pound increase in weight gain adjusting for parental and household variables, sex of the infant, and ethnicity (OR, 1.1; 95% CI, 1.0-1.2). At 14 months the association was reversed; the odds of obesity was decreased by 20 percent for every 5-pound increase in gestational weight gain (OR, 0.8; 95% CI, 0.7-1.0), adjusting for several variables include birth BMI and BMI from the previous study month.

Childhood hospitalization

Study characteristics One study, a cohort of children (N = 11,980) born to mothers attending midwifery centers in Denmark from April 1984

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
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TABLE 26. Gestational Weight Gain and Childhood Weight Status

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Li et al., 2007134

Pregravid weight: Self-report

Maternal weight gain categories (kg):

G1: < 15 lbs

G2: 15-24 lbs

G3: 25-34 lbs

G4: 35-44 lbs

G5: > 45 lbs

AOR (95% CI) for early onset overweight (early onset of overweight that persisted throughout childhood) compared with normal (low probability of overweight throughout childhood and was characterized as the never overweight class)

G5: 1.7 (1.0-2.9)

G3: 1.0 (reference)

Infant sex, race, birth order, gestational age, birthweight, breastfeeding, pregravid BMI, maternal age, maternal education, family income

USA, National Longitudinal Survey of youth 1979 Child and Young Adult file

Total weight gain: Self-report

1,739

Other AOR for weight gain categories for early onset overweight not significant compared with weight gain 25-34 lbs

All weight/BMI

Fair

No association between maternal weight gain and risk of late onset overweight (moderately high probability of overweight at age 2 years, low probability of overweight at age 4 and 6 years, but growing probability of overweight after age 8 years)

Oken et al., 200724

Pregravid weight: Self-report

Maternal weight gain, 5 kg increments

AOR (95%CI) BMI ≥ 95th percentile vs BMI < 50th percentile associated with a 5 kg increase in gestational weight gain:

1.52 (1.19-1.94)

Smoking, race, household income, marital status, glucose tolerance, gestation length, breastfeeding duration, child’s sex

USA, HMO

1,044

Total weight gain: Measured

All weight/BMI

Child BMI z-score at age 3 years for AOR listed above (95% CI):

0.11 (0.05, 0.17)

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Results

Confounders and Effect Modifiers Included in Analysis

Ong et al., 2000133

Pregravid weight: Self-report

Maternal weight gain, continuous measure

Children were grouped into three growth categories (catch-up, no change, and catch-down) based on a gain in weight (SD score > 0.67 for catch-up; SD score < 0.67 for catch-down.

NA

UK, Avon longitudinal study of pregnancy and childhood

Total weight gain: Obstetric records

Maternal weight gain was not a significant predictor of catch-up growth between 0 and 2 years

848

All weight/BMI

Fair

Sowan et al., 2000132

Pregravid weight: Self-report

Maternal weight gain, 5 lb. increments

AOR (95%CI) for infant obesity (BMI > gender and age specific 84th percentile based on Infant Growth Study population norms) at 1, 4, 7, and 10 months: NS

Maternal age, nonpregnant weight, smoking, marital status, father living in home, family stress, grandmother living in home, socioeconomic status, gender, race, infant BMI at birth, infant BMI from previous study month

USA, NIH-funded Infant Growth Study

Total weight gain: Self-report

AOR (95%CI) for obesity at 14 months: .8 (0.7-1.0)

630

All weight/BMI

Poor

AOR, adjusted odds ratio; BMI, body mass index; CI, confidence interval; G, group; HMO, health maintenance organization; kg, kilogram; lbs, pounds; USA, United States of America; vs, versus.

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

to 1987, examined the effect of maternal prenatal lifestyle factors on children’s hospitalizations with infectious diseases (Evidence Table 33).135 After excluding stillbirths, multiple births, and children with congenital malformations, the authors followed 10,440 newborns from 6 months to 12 years. Information on prenatal factors was self-reported by the mother via a questionnaire. Weight gain, calculated as the difference between the self-reported pregravid weight and the weight measured at the time of delivery obtained from the medical records, was categorized as < 10, 10 to 12, 13 to 15, and ≥ 16 kg. Outcome data on hospitalizations related to infections were obtained from registry information based on ICD codes.


Overview of results One fair study suggested that weight gain > 13 kg only for women who were underweight before pregnancy (BMI < 18) was associated with an increased risk of childhood hospitalization for infectious diseases.135


Detailed results The crude incidence rate ratios (IRRs) for the effect of weight gain on hospitalizations were nonsignificant compared with weight gains of 13 to 15 kg: < 10 kg, 0.99; 10 to 12 kg, 0.93; and > 16 kg, 1.01). When maternal pregravid weight status was stratified as BMI < 18 and BMI ≥ 18, weight gain greater than 13 kg among women with a pregravid BMI < 18 increased the risk of hospitalizations compared with women with higher BMI and gaining similar weight (IRR, 1.42; 95% CI, 1.09-1.86). This model adjusted for maternal and paternal age, social group, marital status, number of siblings, and maternal smoking during pregnancy.

Short- and Long-term Maternal Outcomes

Lactation We found no evidence on the effect of gestational weight gain (not defined by IOM definitions) on lactation that accounted for pregravid weight. We present results for studies relying on IOM definitions of weight gain under KQ 3.

Postpartum weight retention

Study characteristics Twelve articles from 10 study populations examine the relationship between gestational weight gain and postpartum weight retention (Evidence Table 34, Table 27).105,136-146 Six articles used data collected within 1-year postpartum;105,140-143,145 four used long-term follow-up data of greater than 1 year postpartum;136,142,144,146 and three used interpregnancy interval data.137-139


Overview of results The results of the two good144,147 and eight105,136-143,145 fair studies reviewed in this section suggest that gestational weight gain is positively associated with weight retention within 1 year postpar-

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

TABLE 27. Gestational Weight Gain and Postpartum Weight Retention

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Callaway et al., 2007146

Pregravid weight: Self report

G1: Gestational weight gain ≤ 15 kg

Australia, University Hospital

Total weight gain: Obstetric records/maternal questionnaires

G2: Gestational weight gain > 15 kg

3,572

All weight/BMI

Good

Harris et al., 1999144

Pregravid weight: Measured at first trimester prenatal visit

Continuous maternal weight gain, kg

UK, Antenatal Care Project

74

Total weight gain: Self report

All weight/BMI

Good

Harris et al., 1997137

Pregravid weight: Measured within 13 weeks’ gestation

Gestational weight gain during previous pregnancy (kg), continuous

UK, Hospital

523

Total weight gain: Measured

All weight/BMI

Fair

Harris et al., 1997138

Pregravid weight: Measured within 13 weeks’ gestation

Gestational weight gain during first pregnancy as a continuous measure (kg)

UK, Hospital

243

Total weight gain: Measured

All weight/BMI

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

G1: Mean change (95% CI) in BMI at 21 years postpartum: 5.06 kg/m2 (4.85-5.27)

Baseline income, secondary school completion, ethnicity, maternal age at birth, parity, birthweight, gestational age, infant sex, maternal smoking during pregnancy, smoking at 21 years, sedentary lifestyle at 21 years, baseline maternal BMI, hypertensive disorders during pregnancy

G2: Mean change (95% CI) in BMI at 21 years postpartum: 6.40 kg/m2 (6.19-6.61)

P < 0.001

G2 was associated with a mean change in BMI over 21 years of 0.19 kg/m2 (95%CI: 0.16-0.22)

ANCOVA model with weight (kg) at 2.5 years postpartum as dependent variable and maternal weight gain (kg) as independent variable:

B = −0.031

β = −0.029

SEM = 0.120

P = 0.796

Marital status, increased dissatisfaction with body, increased access to food, increased energy intake, decreased activity, smoking status, maternal age, duration of followup, pregravid BMI, parity, gestational age at booking, parental obesity, social support

ANCOVA model for interpregnancy weight change (kg), defined as the difference between weight at start of index pregnancy and weight at start of previous pregnancy:

B = 0.262

β = 0.227

SEM = 0.52

P < 0.001

Marital status, smoking status, alcohol, parity, age, socioeconomic status, nulliparous BMI, birthweight, gestational age at start of previous pregnancy, gestational age at start of index pregnancy, gestational age at start of first pregnancy, interpregnancy interval, gestational age at delivery

ANCOVA model for interpregnancy weight change (kg), defined as the difference between weight at start of first pregnancy and weight at start of the second pregnancy:

B = 0.176

β = 0.169

SEM = 0.070

P < 0.013

Marital status, lactation, smoking status, alcohol, height, nulliparous BMI, birthweight, gestational age at start of previous pregnancy, terminations between pregnancy, interpregnancy interval

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Author, Year Country, Setting Sample Size Baseline BMI Quality

Pregravid Weight (How Measured)

Total Weight Gain (How Measured)

Definition of Groups

Hunt et al., 1995139

Pregravid weight: Self-report (validated by hospital records if available)

G1: Population-based sample

USA, population-based family history database (Utah) and participants of an obesity study

G2: Morbidly obese women who were normal weight at age 20-24 years or prior to first pregnancy

Total weight gain: Self-report (validated by hospital records if available)

221

All weight/BMI Morbidly obese

Fair

Linne et al., 2004142

Pregravid weight:

Gestational weight gain as a continuous variable (kg):

Sweden, Stockholm Pregnancy and Weight Development Study

Self-report

G1: Pregravid BMI ≤ 25

Total weight gain: Medical Records

G2: Pregravid BMI > 25

563

All weight/BMI

Fair

Linne et al., 2003136

Pregravid weight: Self-report

G1: Women with normal BMI (20-25) at prepregnancy and 15 years postpartum

Sweden, Stockholm Pregnancy and Women’s Nutrition Study

Total weight gain: Medical records

G2: Women with normal BMI at prepregnancy who had overweight BMI (> 25) at 15 years postpartum

563

Normal weight/overweight

Fair

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×

Results

Confounders and Effect Modifiers Included in Analysis

Regression of current weight on total number of pregnancies showed a 1.3 kg/pregnancy increase in current weight (P = 0.03) with no difference between G1 and G2 (P = 0.60)

Weight at ages 20 to 24, current age

Gestational weight gain was significantly greater in G2 than G1 for the first pregnancy only (P < 0.05)

G2 had a net weight retention after the first pregnancy of 4.0 kg greater than G1 at 6 weeks postpartum

G2 averaged 1.6 kg/pregnancy greater weight retention than G1 for additional pregnancies

G2 had significantly greater weights at prepregnancy, delivery, 1 year postpartum, and 15 years postpartum compared to G1 (P < 0.001); however, G2 did not have a higher risk of postpartum retention than G1

Alcohol use, smoking, number of pregnancies since index child, employment area

G1: Mean (SD) maternal weight gain, 13.6 (3.7) kg

None

G2: Mean (SD) maternal weight gain, 15.4 (4.4) kg

t-Test: P < 0.001

Suggested Citation:"Appendix E: Results from the Evidence-Based Report on Outcomes of Maternal Weight Gain." Institute of Medicine and National Research Council. 2009. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/12584.
×