D Tables of Odds Ratios: Supplement to Chapter 3

Carol J.R. Hogue

Member, Committee on Unintended Pregnancy

Chapter 3 includes an assessment of the literature published within the last 30 years that addresses various health and health-related consequences of unintended pregnancy. The literature base for most consequences studied does not permit a numerical survey. However, some effects, particularly ones related to pregnancy and pregnancy outcome, have been studied sufficiently to permit a structured assessment. These consequences include timing of the initiation of prenatal care, an estimate of the adequacy of prenatal care based on both timing and the number of visits, exposure of the fetus to smoking and alcohol, and the incidence of low birthweight (<2,500 grams) among live-born infants. A graphical presentation of studies on these issues is provided in Chapter 3.

This appendix provides more detail regarding those studies. To be included in this structured assessment, an investigation had to compare outcomes between women reporting intended conceptions and women reporting unintended conceptions, variously defined. When unintended was subdivided into mistimed and unwanted, estimates of effects (usually odds ratios) are included for both categories of unintended conception. An odds ratio is an estimate of the relative risk, that is, the risk of a poor outcome among the "exposed" group (unintended conception) relative to the risk of a poor outcome among the "unexposed" group (intended conceptions). These results, with 95 percent confidence intervals, are shown in column 5 of the tables in this appendix. The results in Figures 3-3 through 3-5 of Chapter 3 were selected from these results. If a study calculated both a crude and an adjusted odds ratio, only the adjusted one was included in the figure. When the results were available for both mistimed and unwanted conceptions, they were included in the figures. The references for this appendix are provided in Chapter 3.



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--> D Tables of Odds Ratios: Supplement to Chapter 3 Carol J.R. Hogue Member, Committee on Unintended Pregnancy Chapter 3 includes an assessment of the literature published within the last 30 years that addresses various health and health-related consequences of unintended pregnancy. The literature base for most consequences studied does not permit a numerical survey. However, some effects, particularly ones related to pregnancy and pregnancy outcome, have been studied sufficiently to permit a structured assessment. These consequences include timing of the initiation of prenatal care, an estimate of the adequacy of prenatal care based on both timing and the number of visits, exposure of the fetus to smoking and alcohol, and the incidence of low birthweight (<2,500 grams) among live-born infants. A graphical presentation of studies on these issues is provided in Chapter 3. This appendix provides more detail regarding those studies. To be included in this structured assessment, an investigation had to compare outcomes between women reporting intended conceptions and women reporting unintended conceptions, variously defined. When unintended was subdivided into mistimed and unwanted, estimates of effects (usually odds ratios) are included for both categories of unintended conception. An odds ratio is an estimate of the relative risk, that is, the risk of a poor outcome among the "exposed" group (unintended conception) relative to the risk of a poor outcome among the "unexposed" group (intended conceptions). These results, with 95 percent confidence intervals, are shown in column 5 of the tables in this appendix. The results in Figures 3-3 through 3-5 of Chapter 3 were selected from these results. If a study calculated both a crude and an adjusted odds ratio, only the adjusted one was included in the figure. When the results were available for both mistimed and unwanted conceptions, they were included in the figures. The references for this appendix are provided in Chapter 3.

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--> TABLE D-1 Studies of Prenatal Care Attainment Associated with Pregnancy Intention Definition of Intention Population/Sample Retrospective/Prospective Control Factors Results Reference/Comments Initiation of Prenatal Care (PNC) after the First Trimester       Unwanted: (a) at conception, (b) at fourth month, (c) in last trimester 120 black women, Boston City Hospital, married with at least one living child, 1964 Prospective at three points during gestation None Late PNC, (a) ORa = 2.89 (0.96,9.02)c, (b) OR = 3.57 (1.38,9.36)c , (c) OR = 2.42 (0.65,9.31)c Watkins, 1968; (a) 77.5%, (b) 27.9%, (c) 11.7%             (a) Mistimed, (b) unwanted NSFG, 1982 (random sample of U.S. women 15–44, with live births 1979–1982) Retrospective (œ3 yrs. postpartum) Race (a) RRb, all = 1.6c; RR, white = 1.6c; RR, black = 1.4c (b) RR, all = 1.8c; RR, white = 1.7c; RR, black = 1.75c Pamuk and Mosher, 1988             "Intended" vs. "unintended" NNS, 1980 (random sample of U.S., married) Retrospective (>6 mo postpartum) Race, residence, education, birth order Crude OR = 1.25c Adjusted OR = -1.19c Wells et al., 1987             Planned vs. unplanned 416, central Harlem residents in PNC, 1982–1983 Retrospective (at first PNC visit) None OR = 1.31c McCormick et al., 1987; 73% were unplanned

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--> Definition of Intention Population/Sample Retrospective/Prospective Control Factors Results Reference/Comments Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended NLSY, 1984, women 18–26, nationally representative sample of 6,015 Retrospective (78%), prospective (22% during pregnancy) Race, economically disadvantaged (white), southern or urban resident at age 14, grandmother's education, maternal age For unintended, crude RR = 1.14c; adjusted OR = 1.6c Marsiglio and Mott, 1988; they used the term "wanted" but the questions more closely reflect intended             "Intended" vs. "unintended" Random sample, 1,490; births in England, 1,984 Retrospective (>4 mo postpartum) None Risk of entry after first trimester; OR = 1.9 (1.33,2.17)c Cartwright, 1988; interview asked pregnancy intention             (a) Mistimed, (b) unwanted NMIHS, 1988 nationally representative sample of 9,953 Retrospective (at least 1 yr postpartum) None (a) RR = 2.88c (b) RR = 2.62c Kost et al., 1994             (a) Mistimed, (b) unwanted Oklahoma PRAMS, 1988–1993, (a) N = 2,329 (b) N = 933 Retrospective (4–12 mo postpartum) Age, education, source of family income, timing of pregnancy recognition, parity (a) Crude OR = 2.7 (2.1,3.4); adjusted OR = 1.4 (1.04,1.9) (b) crude OR = 4.6 (1.3,6.1); adjusted OR = 1.7 (1.1,2.5) DePersio et al., 1994             Planned vs. "surprise" Hispanic, Houston, TX, public hospital patients, 100 each entered PNC in 1st, 2nd, 3rd trimester or none Retrospective (at delivery) None Risk of entry after first trimester OR = 2.64 (1.50,4.66)c Byrd, 1994; early PNC associated with hospital access card, fewer perceived barriers, more benefits to baby             Inadequate Prenatal Care (PNC)         See Results column Random sample in Oklahoma, births, 1985 Retrospective (at delivery) Multiple Receipt of inadequate care, mistimed, family support OR = 1.15c (NS); mistimed, pregnancy discussed OR = 1.09c (NS); unwanted, family support, OR = 1.15c (NS); unwanted, pregnancy discussed, OR = 1.36 (p < 0.05) St. John and Winston, 1989; see text             Unwanted Case—control study, three sites in Missouri; adequate, N=720; inadequate, N=764 Retrospective (at delivery) Multiple Receipt of inadequate care; OR = 1.39 (1.11, 1.67) Sable, 1992; 74% of women with inadequate care had not wanted the pregnancy

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--> Definition of Intention Population/Sample Retrospective/Prospective Control Factors Results Reference/Comments Initial attitude: negative, mixed, or positive 200 poor, mainly black women, Detroit, MI Retrospective (at delivery) Attitudinal Zero-order correlation = 0.39 (p < 0.05) Poland et al., 1990             Planned vs. unplanned; somewhat/very unhappy vs. neutral/happy Case—control, 400 inadequate care, 100 adequate care, Mecklenburg, NC, 1990–991 Retrospective (at delivery) None For unplanned, OR = 1.86 (1.10,3.18)c for unhappy, OR = 2.2 (0.96,3.70)c Boggs and Miles, 1991; among cases with inadequate care, 81% unplanned and 21.2% unhappy             (a) Mistimed, (b) unwanted Oklahoma PRAMS, 1988–1993 (a) N = 2,092 (b) N = 810 Retrospective (4–12 mo postpartum) Education, marital status, source of family income, timing of pregnancy initiation, parity (a) crude OR = 2.7 (1.9,3.7); adjusted OR = 1.3 (0.8,1.9) (b) crude OR = 5.5 (3.8,8.0); adjusted OR = 1.9 (1.2,3.1) DePersio et al., 1994 NOTE: NSFG (National Survey of Family Growth); NNS (National Natality Survey); NLSY (National Longitudinal Survey of Youth); NMIHS (National Maternal and Infant Health Survey); PRAMS (Pregnancy Risk Assessment Monitoring System); NS (not significant). a   The OR (odds ratio) is the odds of adverse outcome among exposed persons relative to the odds among unexposed persons. b   The RR (relative risk) is the risk of the adverse outcome among exposed persons relative to the risk among unexposed persons. Relative risk and odds ratios are similar when adverse outcome is rare. c   Calculated for this report.

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--> TABLE D-2 Studies of Behavioral Risk Factors for Low Birthweight or Preterm Delivery Associated with Pregnancy Intention Definition of Intention Population/Sample Retrospective/Prospective Control Factors Results Reference/Comments Smoking           ''Intended" vs. "unintended" NNS, 1980 (random sample of U.S. married women) Retrospective (> 6 mo post-partum) Race, residence, education, birth order, early PNC Whether didn't stop smoking: crude ORa = 1.13c; adjusted OR = 1.07c Wells et al., 1987; early PNC had similar but independent impact on smoking cessation, as planning the pregnancy did             Planned vs. unplanned 416, central Harlem residents in PNC, 1982–1983 Retrospective (at first PNC visit) None OR = 1.08c McCormick et al., 1987; 41% smoked during pregnancy             (a) Mistimed, (b) unwanted NSFG, 1982 (random sample of U.S. women ages 15–44, with live births 1979–1982) Retrospective (3 yr postpartum) Race (a) RRb, all = 1.3c RR, white = 1.25c RR, black = 1.05c (b) RR, all = 1.3c RR, white = 1.4c RR, black = 1.2c Pamuk and Mosher, 1988

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--> Definition of Intention Population/Sample Retrospective/Prospective Control Factors Results Reference/Comments "Intended" vs. "unintended" Random sample, 1,490; births in England, 1,984 retrospective (>4 mo postpartum) Social class Smoking OR = 1.66 (1.25,2.22)c Cartwright, 1988; interview asked pregnancy intention             Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended NLSY, 1984, women 18–26, nationally representative sample of 6,015 Retrospective (78%) and prospective (22% during pregnancy) Race, economically disadvantaged (white), southern or urban resident at age 14, grandmother's education, maternal age For unintended, crude RR = 1.04c; adjusted OR = 0.97c Marsiglio and Mott, 1988; they used the term "wanted" but the questions more closely reflect intended             (a) Mistimed, (b) unwanted NMIHS, 1988, nationally representative sample of 9,953 Retrospective (at least 1 yr postpartum) Marital status (a) Crude RR = 1.71c (b) crude RR = 1.47c Kost et al., 1994; smoked during pregnancy; married women with wanted conception smoked much less than other subgroups             (a) Mistimed, (b) unwanted Oklahoma PRAMS, 1988–1993 (a) N = 2,267 (b) N = 900 Retrospective (4-12 mo postpartum) Age, education, race, martial status, source of family income (a) Crude OR = 1.3 (1.02, 1.6); adjusted OR = 1.0 (0.8,1.3) (b) crude OR = 2.4 (1.9, 3.1); adjusted OR = 1.8 (1.3,2.4) DePersio et al., 1994; smoking 3 mo before delivery             Alcohol           Planned vs. unplanned 416, central Harlem residents in PNC, 1982–1983 Retrospective (at first PNC visit) None OR = 2.67c McCormick et al., 1987; 9.2% drank during pregnancy

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--> Definition of Intention Population/Sample Retrospective/Prospective Control Factors Results Reference/Comments Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended NLSY, 1984, women aged 18-26, nationally representative sample of 6,015 Retrospective (78%), prospective (22% during pregnancy) Race, economically disadvantaged (white), southern or urban residents at age 14, grandmother's education, maternal age For unintended, crude RR = 1.05c; adjusted OR = 1.25c Marsiglio and Mott, 1988; they used the term "wanted," but the questions more closely reflect intended             (a) Mistimed, (b) unwanted NMIHS, 1988, nationally representative sample of 9,953 Retrospective (at least 1 yr postpartum) None (a) RR = 1.11c (b) RR = 1.77c Kost et al., 1994; drank one or more times per week NOTE: NNS (National Natality Survey); NSFG (National Survey of Family Growth); NLSY (National Longitudinal Survey of Youth); PRAMS (Pregnancy Risk Assessment Monitoring System); NMIHS (National Maternal and Infant Health Survey). a   The OR (odds ratio) is the odds of adverse outcome among exposed persons relative to the odds among unexposed persons. b   The RR (relative risk) is the risk of the adverse outcome among exposed persons relative to the risk among unexposed persons. Relative risk and odds ratios are similar when adverse outcome is rare. c   Calculated for this report.

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--> TABLE D-3 Studies of Low Birth Weight (LBW) (<2,500 grams) Associated with Pregnancy Intention Definition of Intention Population/Sample Retrospective/ Prospective Control Factors Results Reference/ Comments Wanted vs. unwanted 17 selected U.S. sites, 1971–1972; 4,891 white and 3,030 black women Retrospective (at delivery) Race Crude ORa = 1.2c OR for whites = 1.36c OR for blacks = 0.94c Morris et al., 1973; women with high education and unwanted conceptions had babies with significantly higher LBW rates                 Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended NLSY, 1984, women ages 18–26, nationally representative sample of 6,015 Retrospective (78%) and prospective (22% during pregnancy) Race, economically disadvantaged (white), southern or urban resident at age 14, grandmother's education, maternal age For unintended, crude RRb = 1.3c; adjusted OR = 0.92c adjusted OR = 0.88c (including behavioral risk factors) Marsiglio and Mott, 1988                 (a) Mistimed, (b) unwanted NSFG, 1982 (random sample of U.S. women aged 15–44, with live births 1979–1982) Retrospective (œ 3 yr post-partum) Race (a) RR, all = 1.4c RR, white = 1.2c RR, black = 1.3c Pamuk and Mosher, 1988

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--> Definition of Intention Population/Sample Retrospective/ Prospective Control Factors Results Reference/ Comments Unintended vs. intended Case-control study, 1984; 83 LBW cases, 1,392 NBW controls Retrospective (at delivery) Smoking Crude OR = 1.28c adjusted OR = 1.17c (0.70, 1.95)c Cartwright, 1988                 Wanted vs. unwanted 1,518 multiparous, indigent women in Birmingham, AL, 1985–1988, with risk of IUGR Prospective (at PNC visit) None OR = 1.3c Goldenberg et al., 1991; sample was limited to women receiving early PNC                 Mistimed, unwanted 1988 NSFG, most recent singleton birth Retrospective (< 5 yr post-partum) Smoking, race Reduction in LBW if all unwanted conceptions had been avoided Kendrick et al., 1990; mistimed not associated with LBW           No. % change           Black 69,000 7           White 67,000 4           Smoker 70,000 6           Non- smoker 66,000 7   (a) Mistimed, (b) unwanted NMIHS, 1988, nationally representative sample of 9,953 Retrospective (at least 1 yr postpartum) None (a) Crude RR = 1.21c (b) crude RR = 1.80c Kost et al., 1994                 (a) Mistimed, (b) unwanted Oklahoma PRAMS, 1988–1993 (a) N = 2,215 (b) N = 888 Retrospective (4–12 mo postpartum) Education, black race, marital status at delivery, smoking three months before delivery, trimester that PNC began, infant gender, parity, plurality (a) Crude OR = 1.2 (1.1,1.4); adjusted OR = 1.0 (0.8,1.1) (b) crude OR = 1.4 (1.2,1.6); adjusted OR = 0.9 (0.7,1.1) DePersio et al., 1994                 (a) Mistimed, (b) unwanted 1990 NICHD/MOMIH survey Retrospective (>6 mo postpartum) Multiple (a) No increased risk (b) crude OR = 1.44 for LBW adjusted or NS VLBW not associated Sable, 1992 NOTE: NLSY (National Longitudinal Survey of Youth); NBW (Normal birthweight is over 2,500 grams); IUGR (intrauterine growth retardation); NSFG (National Survey of Family Growth); NMIHS (National Maternal and Infant Health Survey); PRAMS (Pregnancy Risk Assessment Monitoring System); NICHD/MOMIH (National Institute of Child Health and Development/Missouri Mothers and Infant Health); VLBW (very low birthweight is under 1,500 grams) a   The OR (odds ratio) is the odds of adverse outcome among exposed persons relative to the odds among unexposed persons. b   The RR (relative risk) is the risk of the adverse outcome among exposed persons relative to the risk among unexposed persons. Relative risk and odds ratios are similar when adverse outcome is rare. c   Calculated for this report.

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