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Total Amount and Pattern of Weight Gain: Physiologic and Maternal Determinants Total weight change during pregnancy can vary from a weight loss to a gain of more than 30 kg (66 lb). This wide variation in gain among healthy pregnant women appears to be attributable to several physiologic and environmental factors. For example, changes in the secretion of mater- nal hormones and other physiologic adjustments associated with pregnancy undoubtedly affect the utilization of energy sources and thus the amount of weight gained. Certain maternal characteristics and health habits may also exert an influence. In this chapter, the subcommittee reviews these physiologic factors and evaluates the relationship between selected mater- nal characteristics and the amount and pattern of gain. A discussion of relationships between dietary- and supplemental energy intake and weight gain is found in Chapter 7. NORMS FOR TOTAL GAIN, RATE OF GAIN, ANI) COMPOSITION OF GAIN Pattern and Amount of Gain In 1971, Hytten and Leitch established physiologic norms for total weight gain, the rate of gain in the last half of pregnancy, and the rate of gain associated with the best reproductive performance. Using data from two British studies (Humphreys, 1954; Thomson and Billewicz, 1957) of more than 3,800 women, they concluded that the physiologic average total gain of "healthy primigravidae women eating without restriction" is 12.5 96

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 28 12 10 8 4 2 A 24 _ ,_ ._ <~ 20 _ ~ Be 16 _ ~ ~ 12 -A 8 Ct -A 4 .-r I I I I I ' ' ' 8 12 16 20 24 28 32 36 40 Week of Gestation 97 FIGURE 5-1 Mean rate of weight gain during pregnancr of 2,868 nonnotensive, pnmi- gravid women, from Thomson and Billewicz (1957) by permission of Blackwell Scientific Publications, Inc. kg (27.5 lb) approximately 1 kg (2.2 lb) in the first trimester and the remainder during the last two trimesters. For multigravid women, they made no specific estimates but suggested that a slightly lower gain could be expected. 1b determine a physiologic norm for rate of gain during the last half of pregnancy, Hytten and Leitch (1971) extracted weight gain data from records maintained by the Aberdeen Maternity Hospital for 486 healthy women aged 20 to 29 and at least 160 cm (63 in.) tall, who delivered their infants between weeks 39 and 41 of pregnancy (between 1950 and 1955). No attempt was made to control weight gain by food restriction in this population. The most common value for the rate of gain during the last half of pregnancy was between 0.41 and 0.45 kg (~1 lb) per week, but the range of gain was very wide from less than 0.1 to 0.9 kg (0.2 to 2 lb) per week. The data from this study are shown in Figure 5-1, which has been used widely to evaluate the rate and total amount of weight gained by pregnant woman. Hytten and Leitch emphasized, however, that considerable variation of this pattern is consistent with good pregnancy outcomes. The lowest incidence of preeclampsia, low birth weight, and perinatal death was associated with gaining 0.45 kgAveek during the last 20 weeks of pregnancy. The following rates were established for each quarter of pregnancy among primigravid women:

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98 NUTRITIONAL STATUS AND WEIGHT GAIN O to 10 weeks, 0.065 kg~week 10 lo 20 weeks, 0.335 kgh~eek 20 to 30 weeks, 0.450 kg/week 30 to 40 weeks, 0.335 kg/week Components of Gain The components of gain can be divided into two parts the products of conception and maternal tissue accretion. The products of conception comprise the fetus, placenta, and amniotic fluid. On the average, the fetus represents approximately 25% of the total gain, the placenta about 5%, and the amniotic fluid about 6% (Hytten, 1980b). Cross-sectional data indicate that fetal growth follows a sigmoid curve, with growth slowing in the final week of gestation. The rate of placental growth declines toward the end of pregnancy. Expansion of maternal tissues accounts for approximately two-thirds of the total gain. In addition to increases in uterine and mammary tissue mass, there is an expansion of maternal blood volume, extracellular fluid, fat stores, and possibly other tissues. In laboratory animals, an increase in liver and intestinal mucosal mass during gestation is evident, but there is no evidence that these tissues increase in pregnant women. Expansion of the blood volume accounts for 10% of the total gain. The increase in plasma volume (approximately 50%) is greater than that of the red blood cell mass increase, but expansion of both is related to fetal size (Hytten, 1980b). Most of the increase in plasma volume occurs before week 34 of gestation; the increase in red blood cell mass is believed to be linear from the end of the first trimester to term. Iron supplementation increases the expansion of the red blood cell mass (see Chapter 14~. In women without generalized edema or with only leg edema, an expansion of the extracellular, extravascular fluid volume accounts for approximately 13% of the total gain. The retention of extracellular fluid can be highly variable; some women accumulate more than 5 liters (5 kg, or 11 lb). The physiologic basis for extracellular fluid retention is uncertain. Placental estrogens may increase the affinity for water of muco- or glycopolysaccharides in connective tissue (Hytten, 1980b), resulting in an expanded, softer tissue. Women normally accumulate fat during pregnancy. Hytten (1980b) estimated that pregnant women who gain 12.5 kg (27.5 lb) without edema acquire about 3.5 kg (7.5 lb) of fat. (See Chapter 6 for other, more recent estimates.) The purpose of the fat store is uncertain: it may be a maternal energy reserve for use when the food supply is limited during either pregnancy or lactation.

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 14 12 10 y ~8 ._ ._ 4 2 0 10 20 Week of Gestation Water 6 Fat _ . _ Protein 30 40 FIGURE 5-2 Composition of weight gain during pregnancy. From Hytten (1980b). Proximate Composition of Gain 99 Hytten (1980b) estimated that, on average, water contributes approx- imately 62% of the total gain at term, fat contributes 30%, and protein contributes 8%; but there is considerable variation in these values. Of the total fat gain, 90% is deposited as maternal stores. About 60% of the total protein accretion is located in the products of conception; the remainder is accounted for by the gain of maternal uterine, mammary, and blood tissues. In early nitrogen balance studies, reported protein retentions were higher than could be accounted for by those fetal and maternal tissues. How- ever, recent studies conducted in metabolic wards have reported protein retentions comparable to the estimated need for pregnancy. Weight gain attributable to body water is the most variable of the components. A reported positive relationship between the increased total body water and infant birth weight (Hytten, 1980b) suggests that water accumulation is beneficial. An estimate of the pattern of weight composition for each quarter of pregnancy is depicted in Figure 5-2. Variation in the composition of gain is discussed in Chapter 6. TOTAL WEIGHT GAIN ACID PATTERN OF GAIN The most representative data for total weight gain in the U.S. pop- ulation are from the 1980 National Natality Survey (NNS) (TaRel, 1986), which is a probability sample of all live births to U.S. women in 1980. Because of the limited amount of information available from published

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100 NUTRITIONAL STATUS AND WEIGHT GAIN reports, the subcommittee relied heavily on the data from the 1980 NNS to determine the independent effects of maternal characteristics on to- tal weight gain (Kleinman, 1990; Duffel, 1986~. The distribution of gains among white, non-Hispanic, married mothers by body mass index (BMI) (Kleinman, 1990) is shown in Figure 5-3 and Table 5-1. Data from 12 other studies on gestational weight gain are shown in Table 5-2. These studies were selected because they provided data on cumulative increase in maternal weight at various times during pregnancy, thus permitting weight gain patterns to be estimated. These data were obtained from six countries and cover a span from 1925 to 1982. Three of the studies (Brown et al., 1986; Husaini et al., 1986; Kawakami et al., 1977) were reported after release of the Food and Nutrition Board's report, Maternal Nutrition and the Course of Pregnancy (NRC, 1970~. The study by Brown et al. (1986) provides the most recent data regarding women living in the United States. Reported average total gains ranged from 10.1 to 14.9 kg (22 to 33 lb) across samples in these studies. From the published data, it is extremely difficult to identify a physiologic norm for total weight . . gain c unng pregnancy. In the studies summarized in liable 5-2, women were weighed when they entered prenatal care (at 13 or 16 weeks of gestation), then usually once per month until about week 30 of gestation, and more frequently after that. Weight change at specific weeks of gestation was observed or interpolated from these data. In most studies, weight change was based on measured weight at the first visit; in others, it was based on recalled prepregnancy weight. Few studies collected data on weight gain during the first trimester. Most of them excluded women with obvious pregnancy complications, but some studies provided few descriptive data about their samples. Problematic characteristics of some studies include prescribed weight restriction, limitations of samples to poor women, and a complete lack of information about sample selection. Infant birth weight, an important criterion for healthy pregnancy outcome, was rarely considered. Not only did total weight gain differ among studies, as mentioned above, but there were also differences in the amount of weight gained at specific points during gestation (liable 5-2~. In the study by Brown et al. (1986), mean weight gains were higher at each gestational period. Patterns of gain are illustrated in Figure 5-4, which shows the cumulative gain reported in the 12 studies, and in Figure 5-5, which provides data from selected studies of well-nourished women with uncomplicated pregnancies in the United States and the United Kingdom. Although the study designs and populations differed among these studies, the slopes of the lines representing cumulative weight gains were quite similar. As mentioned above, Hytten and Leitch (1971) suggested a gain of 0.41 to 0.45 kg (~1 lb) per week as a reference for the last half of

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102 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 5-1 Mean Total Weight Gain and Coefficient of Variation for White, non-Hispanic, Married Mothers Delivering Live Infantsa Weight Gain, kg, by BMI Number in Mean Weight Coefficient of Percentile Group Sample Gain, kg Variation, % 15th 85th Low 1,027 13.8 37 8.6 18.2 (<19.8) Moderate 2,393 13.8 38 7.7 18.6 (19.~26.0) High 246 12.4 48 6.4 17.3 (26.1-29.0) Very high 280 8.7 97 0.5 16.4 (>29.0) Total 3,946 13.3 45 8.2 17.7 a Based on unpublished data from 1980 National Natality Survey. pregnancy. Similarly, Thomson and Billewicz (1957) concluded from their study of 2,868 normotensive Scottish primigravid women that an average gain of about 0.45 kg (1 lb) per week during the second half of pregnancy was a "sound and realistic average to aim at" (p. 247). Rates of gain observed by Thomson and Billewicz (1957) were 0.467 kglweek (standard deviation iSD] = 0.161) between 20 and 30 weeks of gestation and 0.395 kg/week (SD = 0.213) during weeks 30 to 36. Reported rates of gain of U.S. women during the same time period were lower than those observed in the United Kingdom (Robinson et al., 1943; 1bmpkins and Wiehl, 1951). Robinson and coworkers stressed that normal and overweight patients were told to limit their intake of carbohydrates and fat. The highest rate of gain occurred during the seventh lunar month of gestation (Robinson et al., 1943); between 20 and 28 weeks of gestation, the rate of gain averaged approximately 0.455 kg (1 lb) per week. Only four reports of the rate of gain have appeared since 1971. In a 1977 study of weekly weights of 2,000 pregnant Japanese women, the mean rate of gain was 0.45 kg (1.0 lb) per week between 16 and 24 weeks and 0.48 kg/week between 24 and 32 weeks of gestation (Kawakami et al., 1977). Meserole and colleagues (1984) constructed a graph of the weight gain pattern of 80 pregnant girls aged 19 or less. The slope of the rate of gain for the adolescents was described as steeper than that for adult pregnant women. In a study of 1,000 pregnant women in Indonesia (Husaini et al., 1986), the rate of gain and total gain were lower than those reported in the other studies. The mean prepregnangy weight for the Indonesian women was 44.5 kg (98 lb), substantially less than that of women in the United

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 20 18 16 >` ~5 cn 14 Q - ~ 12 ._ ~ 10 ._ a' _ 8 a) 6 4 2 105 Cummings, 1934 Stander and Pastors, 1940 Kuo, 1941 ~Robinson et al., 1943 ~Scott and Benjamin, 1948 _~ Tompkins et al., 1951 ~ Thomson and Billewicz, 1957 { - Hymen and Leitch, 1971 Venkatachalam et al., 1960 t Kawakamj et al., 1977 Brown et al., 1986 _~ Husaini et al., 1986 1 92~1 932 1 932-1 940 1934 1 940 1 943 1941 -1 944 1 947-1 949 1949- 1 954 1950 1955 1 960 1 977 1979- 1 982 1~= Fox /~ ~ //~/~/~ /// ~ I/ ~ it/ - t~ o 1 1 1 10 12 1 1 1 1 1 1 1 1 1 1 1 1 1 - 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Week of Gestation FIGURE 54 Pattern of maternal weight gain shown by data from 12 studies. States. Brown and coworkers (1986) studied the pattern of gain of 459 low- income women who delivered infants weighing between 3,000 and 4,500 g. The weekly rates of maternal weight gain by this group were higher during the first two trimesters than has been reported in other studies (Table S-2), namely, 0.22 kg (O.S lb) per week during the first trimester and 0.52 kg (1.1 lb) per week during the second trimester, but they were comparable (0.40 kg, or 0.9 lb, per week) during the third trimester. A slowing of weight gain or a slight weight loss has been consistently reported as women approached term (Cummings, 1934; Kuo, 1941; Robinson et al., 1943; Scott and Benjamin, 1948~. Few investigators have evaluated weight gain during the first trimester in detail. Clapp et al. (1988) weighed 20 physically active, well-nourished women serially from before conception to week IS of gestation and showed

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106 NUTRITIONAL STUDIOUS AND WEIGHT GAIN Cummings, 1934 (192~1932) 14 - ~Stander and Pastore, 1940 (1932-1940) ---{O Scon and Benjamin, 1948 (1941 -1944) Tompkins and V~ehl, 1951 (1947-1949) Thomson and Billewicz, 1957 (1949-1954) Hymen and Leitch, 1971 (1950-1955) Brown et al., 1986 (197~1982 8 4 2 o / /// To/ At/ q : / 1 1 1 1 1 1 1 1 1 1 i' // 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Week of Gestation FIGURE 5-5 Pattern of maternal weight gain shown by the six studies in Figure 5-4 that focused on well-nounshed women in Europe and the United States who had uncomplicated pregnancies. that maternal gain averaged 2 kg (4.5 lb) at 7 weeks and 4.3 kg (9.5 lb) at 15 weeks; the average rate of gain from 0 to IS weeks of gestation was 0.29 kg, or 0.6 lb, per week. Weights beyond this period were not given. Thomson and Billewicz (1957) reported that 40% of their population gained their suggested amount of 3.6 to 5.4 kg (8 to 12 lb) during the second trimester, whereas almost 25% gained less. The investigators did not relate the pattern of gain to pregnancy outcome. However, only 14% of their sample gained amounts within the ranges the investigators considered to be ideal for both the second and third trimesters. Thus, the individual experience of many pregnant women is unlikely to fit the pattern depicted in Figure S-1.

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110 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 5-3 Gestational Weight Gain Reported by Maternal Prepregnancy Weight-for-Height Status in Different Studies of U.S. Women Number Total Prepregnancyin Mean Coefficient of Weight for HeightSample Gain, kg Variation, % Reference Very low (<80% of 155 12.6 29 Brown et al., 1981 standard a or 79 9.3 34 Mitchell and Lerner, 1989 BMIb ~ 16.5) Low (8~90~o of 243 12.9 36 Brown et al., 1981 standard or BMI 105 11.2 37 Winikoff and Debrovner, 1981 16.5-19.8) 62 11.7 71 Rosso, 1985 268 14.3 31 Abrams and Laros, 1986 80 14.3 NRC Brown et al., 1986 21 15.5 NR Haiek and Lederman, 1989 283 9.3 33 Mitchell and Lerner, 1989 Normal (9~120~o of 301 ll.Od 31 Gormican et al., 1980 standard or BMI 247 12.6 63 Brown et al., 1981 > 19.~26) 106 10.4 32 Winikoff and Debrovner, 1981 35 12.6 33 George et al., 1984 137 10.4 61 Rosso, 1985 1,535 15.2 31 Abrams and Laros, 1986 174 13.9 NR Brown et al., 1986 868 14.4 39 Muscati et al., 1988 39 15.8 NR Haiek and Lederman, 1989 362 8.4 37 Mitchell and Lerner, 1989 High (12~135% of 901 15.2 35 Abrams and Laros, 1986 standard or BMI > 2~29) Very high (>135% 224 14.1 55 Abrams and Laros, 1986 of standard or 68 ~9.7 NR Brown et al., 1986 BMI > 29) a Standards varied among the studies. Weight-for-height tables from Metropolitan Life Insurance Company (1959) were used most commonly. b BMI = body mass index, metric units. c NR = Not reported. d Weight gain for second and third trimesters only. and Lerner (1989) found that the gain of women in the low and very low weight-for-height groups was significantly greater than that of normal- weight women (9.3 compared with 8.5 kg, or 20.5 versus 19 lb). Brown and coworkers (1981) did not find any differences in gain between underweight and normal-weight women. Abrams and Laros (1986) compared the weight gain of women in low, normal, high, and very high weight-for-height groups. No statistically significant differences in mean weight gain were found among women in the four groups, but the total gain of women in the

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 111 very overweight group tended to be slightly lower than that of women in the normal and high groups (14.1 compared with 15.2 kg, or 31 versus 33 lb). These investigators noted that the gains of the women in the very overweight category were more variable than those of women in the other groups. Their coefficient of variation for gain was 55% compared with about 31 to 35% in the other three groups. Among the very overweight women in that study, there was a higher percentage of women with low weight gains, which lowered the group average. The very overweight women in this clinic were not told to limit their food intake or to restrict their weight gain. In these 10 studies, weight gain by women in each of the five groups varied substantially (Table 5-3), and coefficients of variation of gain for women with normal prepregnancy weights ranged from 31 to 63%. This degree of variation in gain after controlling for differences in maternal body size shows that maternal prepregnanc,, weight-for-height status accounts for only a small part of the variation in weight gain. An analysis of the 1980 NNS data (Kleinman, 1990, and Table 5-1) showed that as maternal prepregnancy BMI increased from moderate to very high, mean total weight gain fell by about 5 kg (11 lb), and the variation in gain increased. More than 10% of the women in the very overweight group lost weight during gestation, and more than one-third of the women in that group met the criterion for low weight gain, i.e., a gain of less than 6.8 kg (15 lb). The proportion of women with a low total weight gain was about four times greater among women in the very high BMI group than among women in the low and moderate BMI groups. As shown in Figure 5- 3, only 25% of those with a low BMI, 20% of those with moderate and high BMIs, and 13% of those with very high BMIs had weight gains close to the gain suggested by Hytten and Leitch (1971), i.e., between 11.8 and 13.6 kg, or 26 and 30 lb. The 1980 NNS study is compatible with the observations of Abrams and Laros (1986) that the gains of very overweight women are lower on average and are more variable than those of other women, but it provided no evidence that underweight women were at an increased risk of low weight gain. This is an interesting finding, and follow-up studies are needed. There are only a few studies of the effect of prepregnancy body weight on the panem of weight gain. In one recent study, Meserole and coworkers (1984) compared the pattern of gain of underweight, normal, or overweight adolescents (total sample size, 80~. The only difference observed was a gain by the normal-weight adolescents in the first trimester in comparison with little or no gain by adolescents in the other two groups, but the methods used to ensure the accuracy of the estimates of prepregnancy weight, and thus of early weight gain, were not described. The rate of gain by the normal-weight adolescents was slightly lower in the second and

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112 NUTRITIONAL STATUS AND WEIGHT GAIN third trimesters than that of the underweight and overweight adolescents; total weight gains did not differ. There was no further interpretation of these data, and the differences in weight gain pattern were not tested for significance. Results from studies conducted in the 1940s and 1950s of the effect of prepregnancy weight for height on the rate of gain were inconsistent (Robinson et al., 1943; Scott and Benjamin, 1948; Stander and Pastore, 1940; Thomson and Billewicz, 1957~. Maternal Height In a comprehensive review of the literature, the subcommittee located only one study (Kleinman, 1990) designed to determine whether there is an independent effect of maternal height on total weight gain. In this study, data from the 1980 NNS were analyzed by using multiple linear regression techniques to control for BMI, age and parity, education level, alcohol use, ethnic origin, and cigarette smoking; a significant effect of height on weight gain was observed. Short women (<157 cm, or <62 in.) gained about 1 kg (2 lb) less, on average, than did taller women (>170 cm, or >67 in.), but there was no evidence that short women had an increased risk of low weight gain. An earlier study focused on the relationship between height and the pattern of gain (Thomson and Billewicz, 1957), but no effect was identified. The independent effect of stature on the amount and rate of gain needs further investigation. Ethnic Origin Differences in the total amount of weight gained by black and white women during gestation were first reported by Eastman and Jackson (1968) in a study of clinic patients in Baltimore, Maryland, between 1954 and 1961. The total weight gain of the white women averaged 9.9 kg (21.8 lb), whereas that of the black women averaged 9.0 kg (19.8 lb). The statistical significance of this difference was not determined. The reported mean weight gains of the women of both races was the same if the prepregnancy weight was greater than 82 kg (180 lb). In two other large studies of weight gain conducted in the 1950s and 1960s, no difference in weight gain between black and white women was detected (Niswander and Jackson, 1974; Simpson et al., 1975~. Both black women and white women in the Collaborative Perinatal Project gained an average of 9.9 kg (21.8 lb) (Niswander and Jackson, 1974~. Similar gains were reported for black as well as white wives of military men studied in San Antonio, Texas, between 1946 and 1966 (Simpson et al., 1975~. Multivariate analysis was not used in either of these studies to determine whether there was a statistically significant, independent effect of race on gestational weight gain.

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 113 More recent studies have focused on the effect of ethnic origin on weight gain in populations including white, black, Southeast Asian, and Hispanic women. In an obstetric clinic for teenagers in San Diego, Califor- nia, there was no significant difference in the mean weight gain of white, black, and Hispanic mothers (Felice et al., 1986~; but Hispanic mothers tended to gain the most weight. In another study, Puerto Rican teenagers in New Jersey gained significantly less than white or black teenagers did (Scholl et al., 1988~. In Minnesota, Swenson et al. (1986) studied the weight gains of white, black, Hmong (a Laotian tribe), and other Southeast Asian pregnant adolescents and adults. The total gain of the Hmong and the other Southeast Asian adolescents and adults was about 5 kg (11 lb) less than that of their white and black counterparts. Different attitudes about food practices during pregnancy among Southeast Asian women may contribute to their lower weight gains. The average weight gain of white women in the 1980 NNS was signifi- cantly greater than that of black women (13.2 versus 12.2 kg, or 29.1 versus 26.8 lb) Duffel, 1986~. After controlling for the effects of prepregnancy weight, marital status, education, and age combined with parity, white women still gained about 0.5 kg more than black women did. The gesta- tional period of white women tended to be about 0.5 week longer than that of black women, but this difference only partly explained the higher gains of the white women. The mean weight gain of married Hispanic women and white women did not differ, but the risk of low weight gain was twice as high in Hispanics as it was in whites. Black women also were at a 7055 greater risk for low levels of weight gain compared with whites. In summary, a consistent effect of ethnic origin on gestational weight gain is not apparent in the literature. Black women in the 1980 NNS gained significantly less than white women did. Differences in the gestational period did not account for all this difference. The effect of maternal ethnic origin on the rate of weight gain has not been studied. Age and Parity There are many reports of weight gain and pregnancy outcome in adolescent women, but most do not control for parity, prepregnangy weight for height, gestational length, ethnic origin, or alcohol and tobacco con- sumption when evaluating the effect of age on weight gain. The results of nine studies of weight gain among adolescents published since 1970 are summarized in Able 54. Adolescent mothers in Lima, Peru, gained from 1 to 7 kg (2 to 15 lb) less than U.S. adolescents on the average (Frisancho et al., 1983), but the study is of value because of the large number of pregnant teenagers of each year of age between 12 and 17. The mean weight gains of the Peruvian teenagers between ages 14 and 17 did not differ. Only 28 girls

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114 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 5-4 Effect of Chronological Maternal Age on Gestational Weight Gain Number in Weight Coefficient of ReferenceAge, yr Sample Gain, kg Variation, % Ancri et al., 197712-17 26 13.4 26 1~19 22 12.4 31 2~24 24 11.1 17 25-32 26 10.7 18 Frisancho et al., 198312-13 28 9.0 18 14 104 9.8 22 15 296 9.9 26 16 565 9.7 25 17 229 10.0 26 18-25 46 9.7 16 Horon et al., 1983<16 422 12.5 NRa 2(~24 422 12.5 NR Loris et al., 198513-15.9 18 17.2 23 1~17.9 84 17.1 40 18-19.5 25 17.3 54 Meserole et al., 198413-15 24 14.5 32 1~17 25 17.9 35 Endres et al., 198515-18 46 12.0 NR 19-30 198 11.0 NR Muscati et al., 19881~17 90 16.5 36 1~19 135 15.1 36 2~35 461 13.8 39 Scholl et al., 198816.9 + 1.3 (SD)b 696 14.7 39 Haiek and Lederman, 1989<16 90 14.6 NR 19-30 90 16.9 NR a NR = Not reported. b SD = Standard deviation. were between the ages of 12 and 13, but these girls gained about 0.8 kg (1.8 lb) less than the older girls did. This difference was not tested for statistical significance. No consistent relationship between maternal age and weight gain was observed in the six studies of U.S. women. Three groups reported that young mothers gained more weight (Ancri et al., 1977; Endres et al., 1985; Muscati et al., 1988), two reported that young mothers gained less weight (Haiek and Lederman 1989; Meserole et al., 1984), and two found no difference (Horon et al., 1983; Loris et al., 1985~. One group reported a relationship between gynecologic age and weight gain; immature girls had lower gains than the more mature girls did (Meserole et al., 1984~. This finding, plus the observation that 12- to 13-year-old Peruvian mothers gained less weight (Frisancho et al., 1983), suggests that the weight gains of very young adolescents (<2 years after menarche) may be lower than those of older adolescents. Further research is needed to confirm this conclusion.

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TOTAL AMOUNT AND PATTERN OF WEIGH GAIN 115 Multiple linear regression analysis was used to evaluate the effect of age and parity on weight gain among women who participated in the 1980 NNS (Kleinman, 1990~. Primiparous women lit all age groups gained about 1 kg (2 lb) more than multiparous women of the same age did, and the risk of low weight gains was about one-third lower among primiparous women. After controlling for parity, differences in weight gain by age were small. Primiparous women of all ages gained more (about 1 kg, or 2 lb) than multiparous women of the same age. In summary, the limited data suggest that very young mothers have lower gains than other women do. The effect of pregnancy after age 35 or 40 on gestational weight gain has not been studied. Thomson and Billewicz (1957) studied the relationship between maternal age and the pattern of weight gain, and no relationship was found. Cigarette Smoking Results of multivariate analysis showed that the mean weight gain of married smokers and nonsmokers in the 1980 NNS were similar, but mothers who smoked cigarettes were 50% likelier to gain less than 6.8 kg (15 lb) than were nonsmoking mothers. Rush (1974) and Davies et al. (1976) reported that female nonsmokers gain less weight than female smokers do, but other investigators have not found this effect (Carruth, 1981; Meyer, 1978; Picone et al., 1982~. It appears that smoking has a small effect, if any, on mean gestational weight gain but a larger effect on risk of low weight gain. Alcohol and Illegal Substances There are many reports on the effect of maternal alcohol consumption on fetal growth and development, but few on the relationship between alcohol consumption and gestational weight gain. In a study of 204 alcohol abusers and 11,123 alcohol nonabusers (Sokol et al., 1980), no differences were found in maternal prepregnancy weight, height, or gestational weight gain between the two groups. In another study of 270 pregnant women (Tennes and Blackard, 1980), there was no correlation between alcohol use and gestational weight gain. In the 1980 NNS (Kleinman, 1990), alcohol consumption was found to have little effect on mean weight gain. Mean weight gain of moderate users of alcohol (defined as those who drank more than once per month or more than two drinks per drinking occasion) was 0.2 kg (0.4 lb) higher than that of women who consumed no alcohol. The risk of low weight gain was greatest among the nondrinkers. In a thorough review of the literature, the subcommittee found only one study (Zuckerman et al., 1989) on the relationship between the use

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116 NUTRITIONAL STATUS AND WEIGHT GAIN of cocaine and marijuana and gestational weight gain. In that study, Zuckerman et al. (1989) compared 202 marijuana users with 895 nonusers and 114 cocaine users with 1,010 nonusers among women attending the prenatal clinic at Boston City Hospital. The mean weight gain of marijuana users was 12.7 kg (28 lb) compared with 14.1 kg (31 lb) for nonusers. The mean gain of cocaine users was 10.5 kg (23 lb) compared with 14.1 kg (31 lb) for nonusers. The use of these substances and other illicit drugs generally is associated with a life-style that is not supportive of good eating and health habits. Therefore, it is not surprising that these women had lower mean weight gains during pregnancy. Socioeconomic Status Information about family income was requested on questionnaires that were sent to married mothers in the 1980 NNS (Taffel, 1986~. In a bivariate analysis, women from households with incomes above $30,000 per year gained 0.6 kg (1.4 lb) more than did women from households with incomes of less than $9,000 per year. The risk of low weight gain increased nearly twofold as annual household income fell from $30,000 to $9,000. However, these results were not statistically controlled for other variables that could influence weight gain. Marital status is also linked with socioeconomic status since female- headed households tend to have lower household incomes. On the average, married mothers gained about 1 kg more than unmarried mothers did (Taffel, 1986~. Data on the educational attainment of both married and unmarried mothers were analyzed in the multiple linear regression described by Klein- man (1990~. Mean weight gain was similar for women in all educational groups, but compared with mothers with 13 or more years of education, the risk of low weight gain was 50% higher among mothers with <12 years of education and 25% higher among those with 12 years of education. Work or Physical Activity Studies on the effect of heavy work or physical activity on weight gain should be interpreted with caution, because high energy expenditure can be offset by increases in energy intake so that energy balance is maintained. Also, it is difficult to determine whether the stress (both physical and psychologic) of work, instead of the increased energy expenditure, may have led to reduced weight gain. Some investigators have reported an elevated risk of preterm delivery among working women (Mamelle and Munoz, 1987; Mamelle et al., 1984), whereas others have failed to identify such a relationship (Berkowitz et al., 1983; Kaminski and Papiernik, 1974;

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 117 Zuckerman et al., 1986~. If work or physical activity reduced the length of gestation, total weight gain would also be reduced. Measurement of the rate of gain could be used to adjust for differences in the length of gestation. Although many studies have been conducted on the effects of work on pregnancy (i.e., birth weight, gestational duration, and complications of labor and delivery), those few that provide data on weight gain (Naeye and Peters, 1982; Tafari et al., 1980) provide little useful information about the effect of work on weight gain. CONCLUSIONS ANI) RECOMMENDATIONS Since 1970, most reported average total pregnancy weight gains have ranged between 10 and 15 kg (22 and 33 lb). The mean rate of gain during the last half of gestation ranged from 0.45 to 0.52 kg (~1 lb) per week The relatively low energy cost (~4.7 kcaVg) of tissue gain during preg- nancy probably reflects the high concentration of water in the lean tissue that is deposited. Hormonal adjustments that induce changes in the effi- ciency of fuel use for tissue synthesis are possible, but actual measurements of the energy cost for fat or lean tissue synthesis in pregnant women have not been made. Differences in the physiologic response to pregnancy may account for much of the diversity in gains, but certain maternal factors, e.g., high prepregnancy weight for height, short stature, black or Southeast Asian background, very young age (<2 years after menarche), multiparity, un- married status, and low income, are important predictors of a risk of low weight gain. Maternal use of alcohol does not appear to affect weight gain significantly. Furthermore, the limited data available do not show that work outside the home or physical activity affects weight gain in U.S. women. CLINICAL IMPLICATIONS Total weight gain during pregnancy varies widely among women with similar ages, weights, heights, ethnic backgrounds, and socioeconomic status. Gestation gains between the 15th and 85th percentiles range from approximately 7 to 18 kg (16 to 40 lb). Therefore, recommended gains should be used only as targets and for identifying individuals who should be evaluated for insufficient or excessive rates of gain. The observed rate of gain in the second and third trimesters ranges from 0.3 to 0.7 kg (0.7 to 1.4 lb) per week. The average rate of gain during the second trimester may be slightly higher than that during the third trimester. .

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118 NUTRITIONAL STATUS AND WEIGHT GAIN Within a population, the range of gestational weight gains is wider among overweight women than among normal-weight or underweight ~ O _ ~ O women. Although some investigators have reported different rates of gain among teenagers and members of various minority groups, there is no biologic evidence to justify different recommendations for these women. The risk of low weight gain (<6.8 kg, or 15 lb) is higher among unmarried women, black and Hispanic women, cigarette smokers, and women with low levels of education. These women should receive additional nutritional counseling to ensure an adequate weight gain during pregnancy. No evidence was found to suggest that work outside the home or regular physical activity increases the risk of low weight gains during pregnancy. REFERENCES Abrams, B.F., and R.K Laros, Jr. 1986. Prepregnano~r weight, weight gain, and birth weight. Am. J. Obstet. Gynecol. 154:503-509. Ancri, G., E.H. Morse, and R.P. Clarke. 1977. Comparison of the nutritional status of pregnant adolescents with adult pregnant women. III. Maternal protein and calorie intake and weight gain in relation to size of infant at birth. Am. J. Clin. Nutr. 30:568-572. Berkowitz, G.S., J.L Kelsey, T.R. Holford, and R.L Berkowitz. 1983. Physical activity and the risk of spontaneous preterm delivery. J. Reprod. Med. 28:581-588. Brown, J.E., H.N. Jacobson, LH. Askue, and M.G. Peick. 1981. Influence of pregnancy weight gain on the size of infants born to underweight women. Obstet. Gynecol. 57:13-17. Brown, J.E., K.W. Berdan, P. Splett, M. Robinson, and LJ. Harris. 1986. Prenatal weight gains related to the birth of healthy-sized infants to low-income women. J. Am. Diet. Assoc. 86:1679-1683. Carruth, B.R. 1981. Smoking and pregnancy outcome of adolescents. J. Adol. Health Care 2:115-120. Clapp, J.F., III, B.L" Seaward, R.H. Sleamaker, and J. Hiser. 1988. Maternal physiologic adaptations to early human pregnancy. Am. J. Obstet. Gynecol. 159:145~1460. Cummings, H.H. 19S4. An interpretation of weight changes during pregnancy. Am. J. Obstet. Gynecol. 27:808-815. Davies, D.P., O.P. Gray, PC Ellwood, and M. Abernethy. 1976. Cigarette smoking in pregnancy: associations with maternal weight gain and fetal growth. Lancet 1:385-387. Durnin, J.V.G.N 1987. Energy requirements of pregnancy an integration of the longitudinal data from the five-county study. Lancet 2:1131-1133. Eastman, NJ., and E. Jackson. 1968. Weight relationships in pregnancy. I. Ibe bearing of maternal weight gain and pre-pregnangy weight on birth weight in full term pregnancies. Obstet. Gynecol. Sure. 23:1003-1025. Endres, J.M., K. Poell-Odenwald, M. Sawicki, and P. Welch. 1985. Dietary assessment of pregnant adolescents participating in a supplemental-food program. J. Reprod. Med. 30:10-17. Felice, M.E., P. Shragg, M. James, and D.R. Hollingsworth. 1986. Clinical observations of Mexican-American, Caucasian, and black pregnant teenagers. J. Adol. Health Care 7:305-310. Forbes, G.B. 1988. Body composition: influence of nutrition, disease, growth, and aging. Pp. 533-556 in M.E. Shils and V.R. Young, eds. Modern Nutrition in Health and Disease, 7th ed. Lea & Febiger, Philadelphia.

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TOTAL AMOUNT AND PATTERN OF WEIGHT GAIN 119 Frisancho, A.R., J. Matos, and P. Flegel. 1983. Maternal nutritional status and adolescent pregnancy outcome. Am. J. Clin. Nutr. 38:739-746. George, N.N., S.K. Kim, and J.L Duhring. 1984. Prepregnancy weights and weight gains related to birth weights of infants born to overweight women. J. Am. Diet. Assoc. 84:450-452. Gormican, A-, J. Valentine, and E. Satter. 1980. Relationships of maternal weight gain, prepregnancy weight, and infant birthweight. Interaction of weight factors in pregnancy. J. Am. Diet. Assoc. 77:662~67. Haiek, L., and S.A. Lederman. 1989. The relationship between maternal weight for height and term birth weight in teens and adult women. J. Adol. Health Care 10:16-Z. Horon, I.L., D.M. Strobino, and H.M. MacDonald. 1983. Birth weights among infants born to adolescent and young adult women. Am. J. Obstet. Gynecol. 146:444449. Humphreys, R.C. 1954. An analysis of the maternal and foetal weight factors in normal pregnancy. J. Obstet. Gynaecol. Br. Commonw. 61:764-771. Husaini, Y.K., M.~ Husaini, Z. Sulaiman, NB. Jahari, Barizi, S.T. Hudono, and D. Karyadi. 1986. Maternal malnutrition, outcome of pregnancy, and a simple tool to identify women at risk. Food Nutr. Bull. 8:71-76. Hytten, F.E. 1980a. Nutrition. Pp. 163-192 in F. Hytten and G. Chamberlain, eds. Clinical Physiology in Obstetncs. Blackwell Scientific Publications, Oxford. Hytten, F.E. 1980b. Weight gain in pregnangy. Pp. 193-233 in F. Hytten and G. Chamberlain, eds. Clinical Physiology in Obstetrics. Blackwell Scientific Publications, Oxford. Hytten, F.E., and I. Leitch. 1971. The Physiology of Human Pregnancy, 2nd ed. Blackwell Scientific Publications, Oxford. 599 pp. Kaminski, M., and E. Papiernik. 1974. Multifactonal study of the risk of prematurity at 32 weeks of gestation. II. A comparison between an empirical prediction and a discriminant analysis. J. Perinat. Med. 2 37~4. Kawakami, S., ~ Ishiwata, K. Hayashi, Y. Kawaguchi, N. Kondo, and R. Iizuka. 1977. Alteration of maternal body weight in pregnangy and postpartum. Keio J. Med. 26:53~2. Kitzmiller, J.L. 1980. The endocrine pancreas and maternal metabolism. Pp. 58-83 in D. Iblchinsky and KJ. Ryan, eds. Maternal-Fetal Endocrinology. SUB. Saunders, Philadelphia. Kleinman, J.C. 1990. Maternal Weight Gain During Pregnancy Dete~minants and Conse- quences. NCHS Working Paper Series No. 33. National Center for Health Statisti~, Public Health Se~vice, U.S. Department of Health and Human Services, Hyattsville> Md. 24 pp. Kuo, C.C. 1941. Weight gain in normal pregnancy in Chinese patients. Chin. Med. J. 59:278-286. Loris, P., KG. Dewey, and K. Poirier-Brode. 1985. Weight gain and dieta~y intake of pregnant teenagers. J. Am. Diet. Assoc. 85:1296-1305. Mamelle, N., and F. Munoz. 1987. Occupational working conditions and preterm birth: a reliable scoring system. Am. J. Epidemiol. 126:150-152. Mamelle, N., B. Laumon, and P. Lazar. 1984. Prematurity and occupational activity dunng pregnancy. Am. J. Epidemiol. 119:309-322. Meserole, L.P., B.S. Worthington-Roberts, J.M. Rees, and LS. Wright. 1984. Prenatal weight gain and postpartum weight loss patterns in adolescents. J. Adol. Health Care 5:21-27. Metropolitan Life Insurance Company. 1959. New weight standards for men and women. Stat. Bull. Metrop. Life Insur. Co. 40:1-4. Meyer, M.B. 1978. How does maternal smoking affect birth weight and maternal weight gain? Evidence from the Ontario Perinatal Mortality Study. Am. J. Obstet. Gynecol. 131:888-893. Mitchell, M.C., and E. Lerner. 1989. Weight gain and pregnancy outcome in underweight and normal weight women. J. Am. Diet. Assoc. 89 634~38. Muscati, S.K., M.N Mackey, and B. Newsom. 1988. The influence of smoking and stress on prenatal weight gain and infant birth weight of teenage mothers. J. Nutr. Educ. 20:299-302.

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