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Should Obese Women Gain Less Weight in Pregnancy Than Recommended? Reena Oza-Frank, PhD, RD, and Sarah A. Keim, PhD ABSTRACT: Background: Previous research on inadequate gestational weight gain among obese women and adverse outcomes has been mixed. The objective of this study was to examine associations between inadequate gain among obese women and antepartum, intrapartum, and infant outcomes. Methods: Obese women from the U.S. Collaborative Perinatal Project were divided into obesity classes I (30.0–34.9 kg/m2) and II/III (> 35.0 kg/ m2) and three weight gain categories (inadequate: < 5 kg, adequate: 5–9 kg, excessive: > 9 kg) as defined by the U.S. Institute of Medicine. Associations between 1-kg increments of inadequate gain (< 5 kg) and outcomes were examined. Women with inadequate gain were also compared with women gaining normal (5–9 kg) and excessive (> 9 kg) weight. Results: Each fewer 1-kg of weight gain increased small-for-gestational age (SGA) risk and reduced large-for-gestational age (LGA) risk by similar magnitude. Compared with excessive gain, inadequate gain reduced the odds of preeclampsia (OR: 0.56, CI: 0.37, 0.84), gestational hypertension (OR: 0.66, CI: 0.47, 0.92), and LGA (OR: 0.48, CI: 0.38, 060) and increased the odds of SGA (OR: 2.26, CI: 1.52, 3.35). Inadequate gain offered fewer advantages over adequate weight gain: lower odds of LGA (OR: 0.75, CI: 0.57, 0.99); increased odds of SGA (OR: 1.86, CI: 1.18, 2.91). Most associations applied to obesity class I but not class II/III women. Conclusions: Inadequate weight gain poses benefits and risks to mothers and infants, but is preferable to excessive gain. The risks and benefits apply differently to class I versus class II/III obese women, indicating the need for weight gain recommendations by obesity class. (BIRTH 40:2 June 2013)
Key words: Collaborative Perinatal Project, gestational weight gain, infant, obesity, prepregnancy body mass index
Obesity among women of reproductive age in the United States (12–44 years) has increased twofold in the past 30 years, with a current prevalence of nearly 33 percent (1). Women with pre-pregnancy obesity are at increased risk of adverse pregnancy outcomes such as hypertension, preeclampsia, gestational diabetes, more frequent cesarean delivery, delivery of large-for-gestational age (LGA) infants, and stillbirths (2–7). These risks are compounded by excessive gestational weight gain (8), and optimizing weight gain may aid in reducing the risk of adverse outcomes.
In 2009, the United States Institute of Medicine released new recommendations for weight gain during pregnancy (9). Compared with the 1990 guidelines (10), the new recommendations provide an upper weight gain limit for obese women (5–9 kg). Weight gain below 5 kg is considered inadequate, and gain above 9 kg is considered excessive. This recommendation was based on limited available data considering six outcomes: small-for-gestational age (SGA), LGA, caesarean delivery, preterm delivery, postpartum weight retention, and child obesity. These data were primarily
Reena Oza-Frank and Sarah A. Keim are Principal Investigators at the Research Institute at Nationwide Children’s Hospital, Columbus, and Assistant Professors in the Department of Pediatrics, The Ohio State University, Columbus, OH, USA.
Hospital, Department of Pediatrics, The Ohio State University, 700 Children’s Drive, Research Building 3, Columbus, OH 43205, USA.
Address correspondence to Reena Oza-Frank, PhD, RD, Center for Perinatal Research, Research Institute at Nationwide Children’s
© 2013, Copyright the Authors Journal compilation © 2013, Wiley Periodicals, Inc.
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108 from women with body mass index (BMI) values of 30–34.9 kg/m2 (9), and therefore, the committee felt there existed insufficient evidence to provide guidance for women with class II (35–39.9 kg/m2) or class III (40 or more kg/m2) obesity. In addition, weight loss or weight maintenance during pregnancy was not recommended by the committee, regardless of obesity class, because of concern that low weight gains or weight loss would lead to small size at birth and poor neurologic outcomes in the offspring (11). However, it has been reported that although 50–60 percent of overweight and obese women gain more than is recommended, the prevalence of weight loss appears to increase with increasing pre-pregnancy obesity (12). A few recent studies suggest that weight gain of < 5 kg is not associated with deleterious consequences in obese mothers (8,13) and results in lowered risks of some adverse obstetric and neonatal outcomes (14,15). It is important to note that how body size and weight gain are measured and statistical analysis techniques may affect study results. Few studies have examined gestational weight gain as a continuous variable, and this lapse may obscure subtle differences across the range of weight gain values. Also, some obstetric outcomes were not examined by the committee. Therefore, the objective of this study was to examine associations between inadequate weight gain among obese women, including by obesity class and race, and a range of antepartum, intrapartum, and infant outcomes based on data from the prospective U.S. Collaborative Perinatal Project.
Materials and Methods The data are from a large prospective study, which enrolled a diverse sample of women (55,000 pregnancies) at the first prenatal visit at 12 urban U.S. sites, during 1959 to 1965 and followed women and their children to age 8 years (16). This analysis was restricted to women with a pre-pregnancy BMI 30 kg/m2 (n = 5,076), excluding pregnancies with twin or other higher order multiples (n = 254), women without a recorded race or had a race that was not black or white (477; 21 women were missing race and also carrying multiples) and women who were not weighed within 3 weeks of delivery (1,577), leaving 2,789 in the final analytical sample. Maternal pre-pregnancy BMI was calculated using self-reported pre-pregnancy weight at the first prenatal visit and measured height in inches without shoes. Pre-pregnancy BMI was categorized as obesity class I (30.0–34.9 kg/m2), class II (35.0–39.9 kg/m2), or class III ( 40.0 kg/m2). Class II (n = 588) and III (n = 233) categories were combined due to small sample sizes. Weight was measured at each prenatal visit in
street clothes without shoes or a coat. Gestational weight gain, measured both as a continuous and a categorical variable, was the main exposure. Recognizing that there exists no best measure of weight gain during pregnancy (17), weight gain was calculated as measured weight at the last prenatal visit within three weeks of delivery minus pre-pregnancy weight. For gestational weight gain categories, the current Institute of Medicine guidelines were followed, which classify obese women as inadequate (< 5 kg), adequate (5–9 kg), or excess (> 9 kg) gainers according to pre-pregnancy BMI (9). Outcomes observed were risk factors and diseases that have previously been associated with excessive or inadequate weight gain in women of varying adiposity. Maternal outcomes examined included preeclampsia (signified by both hypertension and either proteinuria or one of the following: pulmonary edema, oliguria, or convulsions from 24 weeks’ gestation to 2 weeks postpartum (18)), gestational hypertension (diastolic pressure of 90 mmHg, with onset between 24 weeks’ gestation and 2 weeks postpartum (18)), intrapartum bleeding (> 500 mL), anemia (any single value < 10 g hemoglobin or < 30% hematocrit), and breech presentation. Infant outcomes examined included SGA (birthweight in the 10th percentile or below for race and gender based on the distribution within the cohort for births at > 30 weeks’ gestation) and LGA (birthweight in the 90th percentile, as for SGA) (19). Information on gestational age, calculated on the basis of the last menstrual period, birthweight, and child’s sex was collected from the study obstetric records. Low Apgar score was also included (score < 7 at 5 minutes after birth (20)). Potential covariates identified a priori from other studies are listed in Table 1. For each pregnancy, these data were collected at the first prenatal visit interview. In the regression models, maternal age, education, socioeconomic status (21), and smoking habits (number of cigarettes smoked per day as of the first prenatal visit) were included as continuous variables.
Statistical Analysis To examine the association between weight gain and pregnancy outcomes of interest, generalized estimating equations (GEE) models were used to adjust standard errors for the clustering in the sample because of inclusion of women with more than pregnancy (n = 284). After adjusting for potential confounders, beta coefficients or odds ratios (ORs, unadjusted and adjusted) and 95 percent confidence intervals (CI), were estimated. Because gestational weight gain is likely to be correlated with gestational age at birth (22), the correlation between weight gain and gestational age was examined and gestational age was tested as a confounder in all models
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(except for SGA, LGA models). Finally, overall analyses were restricted to term births (22) to compare with results from models that included all births. Statistical
significance was based on p 0.05. Associations between inadequate weight gain and maternal and infant outcomes were examined using weight gain as a contin-
Table 1. Characteristics of Obese Women According to Categories of Gestational Weight Gain Established by the U.S. Institute of Medicine, Collaborative Perinatal Project, 1959 to 1965
Gestational Weight Gain (kg)
Maternal age (years)* 500 mL Anemia Child outcomes Small for gestational age Large for gestational age Apgar < 7 (5 minutes) Breech presentation
Stratified by Obesity Class
All Women
Black Women
White Women
Class I
Class II or III
0.97 (0.91, 1.04) 0.99 (0.95, 1.03)
0.97 (0.90, 1.05) 0.96 (0.90, 1.02)
0.97 (0.87, 1.08) 1.01 (0.94, 1.08)
0.97 (0.85, 1.10) 1.01 (0.94, 1.08)
0.97 (0.90, 1.05) 0.99 (0.93, 1.05)
0.93 (0.86, 1.00) 1.01 (0.98, 1.04)
0.94 (0.85, 1.04) 1.03 (0.99, 1.07)
0.91 (0.80, 1.03) 0.92 (0.85, 0.99)
0.94 (0.82, 1.08) 1.01 (0.96, 1.06)
0.94 (0.86, 1.02) 1.00 (0.96, 1.04)
1.06 (1.02, 1.10)
1.03 (0.98, 1.08)
1.13 (1.06, 1.21)
1.11 (1.04, 1.17)
1.02 (0.96, 1.08)
0.94 (0.90, 0.98)
0.94 (0.89, 0.99)
0.94 (0.89, 1.00)
0.82 (0.74, 0.90)
1.00 (0.96, 1.04)
0.96 (0.91, 1.01)
—
1.00 (0.93, 1.07)
0.98 (0.89, 1.07)
1.00 (0.94, 1.06)
0.99 (0.93, 1.06)
0.96 (0.85, 1.07)
1.01 (0.92, 1.11)
0.99 (0.81, 1.20)
1.00 (0.93, 1.07)
Models included: infant sex, socioeconomic status, maternal age, maternal education, number of cigarettes smoked per day, parity, gestational age (except SGA, LGA models), race (except models stratified by race), maternal pre-pregnancy BMI (except models stratified by obesity class). — denotes inadequate sample sizes to run GEE models.
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gain compared with class I obese women with adequate weight gain (0.28 [0.10–0.79]) and a lower risk of gestational hypertension (0.57 [0.34–0.94]).
Compared with women with excessive weight gain, women with inadequate weight gain were less likely to have preeclampsia (0.56 [0.37–0.84]), gestational hypertension (0.66 [0.47–0.92]), an LGA infant (0.48 [0.38–0.60]) and more likely to have an SGA infant (2.26 [1.52–3.35]) (Table 3). However, results for gestational hypertension were no longer significant when restricting to term births (0.70 [0.49–1.01]). Both black and white women with inadequate weight gain were less likely to have an LGA infant (0.43 [0.32–0.57] for white women) and more likely to have an SGA infant compared with their counterparts with excessive weight gain. Black women with inadequate weight gain were less likely to have preeclampsia (0.56 [0.33–0.93)], whereas white women with inadequate weight gain were less likely to have gestational hypertension (0.46 [0.25– 0.84]). Class I obese women with inadequate weight gain were less likely to have preeclampsia (0.43 [0.25–0.73]), gestational hypertension (0.55 [0.36–0.85]), or an LGA infant (0.40 [0.30–0.53]) compared with class I obese women with excessive weight gain. Class II/III obese women with inadequate weight gain were less likely to have an LGA infant (0.64 [0.43–0.95]) compared with class II/III women with excessive weight gain. Compared with women with adequate weight gain, women with inadequate weight gain were more likely to have an SGA infant (1.86 [1.18–2.91]) and less likely to have an LGA infant (0.75 [0.57–0.99]) (Table 4). The association with SGA remained similar by race; however, the association was not significant within obesity classes. For LGA, associations did not differ by race or obesity class. Among class I obese women, there existed a lower risk of breech presentation among infants of women with inadequate weight
Discussion We found that gestational weight gain below guidelines, compared with excessive gain, was associated with an increased risk of SGA among class I obese women, but not among class II/III obese women. Inadequate weight gain was also associated with decreased risk of LGA, again when comparing inadequate to excessive weight gain. Overall, inadequate (compared with excessive) weight gain among obese women resulted in reduced risks of maternal complications such as gestational hypertension and preeclampsia. Although our results comparing inadequate to adequate weight gain were not significant for maternal complications or LGA, there existed a trend toward more favorable outcomes among women with inadequate weight gain. This study adds to the previous literature supporting the development of weight gain recommendations specific to obesity class (14,15,24). Comparable to our study, previous studies have also shown an increased risk of SGA with inadequate weight gain among obesity class I women, but not class II/III women (15,25). Other studies have shown that this relationship exists among both class I/II women, but not class III women (14,24). Despite slight differences, these studies indicate that class I obese women may need to gain slightly more weight than class II/III obese women to minimize risk of SGA. Inadequate gestational weight gain, regardless of obesity class, results in reduced risk
Table 3. Associations Between Inadequate (< 5 kg) Compared with Excessive (> 9 kg) Gestational Weight Gain and Maternal and Child Outcomes, Overall and Stratified by Obesity Class (adjusted models), Collaborative Perinatal Project, 1959 to 1965
Stratified by Race All Women Maternal outcomes Preeclampsia Gestational hypertension Bleeding > 500 mL Anemia Child outcomes Small for gestational age Large for gestational age Apgar < 7 (5 minutes) Breech presentation
Black Women
Stratified by Obesity Class
White Women
Class I
Class II or III
0.56 0.66 0.87 1.07
(0.37, (0.47, (0.56, (0.85,
0.84) 0.92) 1.37) 1.36)
0.56 0.84 0.83 1.00
(0.33, (0.56, (0.48, (0.77,
0.93) 1.25) 1.42) 1.30)
0.52 0.46 0.97 1.48
(0.26, (0.25, (0.45, (0.84,
1.02) 0.84) 2.09) 2.59)
0.43 0.55 0.82 1.09
(0.25, (0.36, (0.48, (0.83,
0.73) 0.85) 1.41) 1.43)
0.90 0.79 1.08 0.95
(0.42, (0.42, (0.50, (0.60,
1.92) 1.45) 2.35) 1.50)
2.26 0.48 0.98 0.82
(1.52, (0.38, (0.64, (0.44,
3.35) 0.60) 1.49) 1.54)
2.16 0.43 1.17 0.67
(1.34, (0.32, (0.71, (0.29,
3.48) 0.57) 1.93) 1.52)
2.54 0.56 0.54 1.17
(1.25, (0.39, (0.26, (0.41,
5.13) 0.81) 1.15) 3.29)
2.41 0.40 0.79 0.39
(1.49, (0.30, (0.47, (0.14,
3.87) 0.53) 1.33) 1.07)
1.82 0.64 1.78 1.66
(0.91, (0.43, (0.78, (0.55,
3.64) 0.95) 4.06) 5.01)
Models included: infant sex, socioeconomic status, maternal age, maternal education, number of cigarettes smoked per day, parity, gestational age (except SGA, LGA models), race (except models stratified by race), maternal pre-pregnancy BMI (except models stratified by obesity class).
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Table 4. Associations Between Inadequate (< 5 kg) Compared with Adequate (5–9 kg) Gestational Weight Gain and Maternal and Child Outcomes, Overall and Stratified by Obesity Class (adjusted models), Collaborative Perinatal Project, 1959 to 1965
Stratified by Race All Women Maternal outcomes Preeclampsia Gestational hypertension Bleeding > 500 mL Anemia Child outcomes Small for gestational age Large for gestational age Apgar < 7 (5 minutes) Breech presentation
Black Women
Stratified by Obesity Class
White Women
Class I
Class II or III
0.96 0.70 1.07 1.16
(0.56, (0.48, (0.65, (0.88,
1.65) 1.02) 1.76) 1.53)
1.09 (0.54, 2.19) 1.01 (0.61, 1.68) — 1.10 (0.80, 1.50)
0.76 0.43 3.19 1.56
(0.31, (0.24, (0.98, (0.83,
1.85) 0.77) 10.38) 2.95)
0.81 (0.40, 1.64) 0.57 (0.34, 0.94) — 1.08 (0.79, 1.48)
1.29 0.89 1.22 1.43
(0.50, (0.47, (0.45, (0.81,
3.36) 1.69) 3.32) 2.54)
1.86 0.75 0.90 0.65
(1.18, (0.57, (0.56, (0.33,
2.91) 0.99) 1.44) 1.28)
2.04 0.72 1.05 0.43
2.05 0.71 1.01 0.43
(1.16, (0.48, (0.59, (0.18,
3.59) 1.04) 1.76) 1.02)
1.55 0.81 0.69 1.05
1.65 0.74 0.71 0.28
(0.99, (0.53, (0.40, (0.10,
2.74) 1.05) 1.28) 0.79)
(1.16, (0.49, (0.60, (0.17,
3.59) 1.04) 1.84) 1.07)
(0.74, (0.53, (0.26, (0.32,
3.23) 1.24) 1.81) 3.51)
Models included: infant sex, socioeconomic status, maternal age, maternal education, number of cigarettes smoked per day, parity, gestational age (except SGA, LGA models), race (except models stratified by race), maternal pre-pregnancy BMI (except models stratified by obesity class). — denotes inadequate sample sizes to run GEE models.
for LGA (14,15). It is important to note that this group of women who gained inadequate amounts of weight included both women who lost weight and women who gained < 5 kg, so these results are not directly equivalent to weight loss, where more research is needed. In this study and in others (14,15), risk for preeclampsia was lower among obese women with inadequate weight gains. Preeclampsia is an example of a maternal outcome where pre-pregnancy BMI is a major risk factor (25). Because guidance on weight gain may not modify all preexisting risks in obese women, it is important to balance risks of weight gain for both the mother and the child (11), with the provision of individualized recommendations based on clinical judgment (26). For example, in this study, we provide support that there may be an opportunity to improve different outcomes among class I obese women compared with class II/III obese women. We detected few statistically significant differences in the odds of outcomes between black and white women. Although not statistically significant, there existed a suggestion that the odds of gestational hypertension and preeclampsia among white women who gain an inadequate amount of weight compared with those who gained an adequate amount might be even lower than reported for the cohort overall. A larger study involving a diverse sample of women could confirm and help clarify these and other potential differences by race. Determining a method to measure gestational weight gain and simultaneously account for potential correlations with gestational age at delivery is currently under discussion (22). Total gestational weight gain and other measures (i.e., average rate of gestational weight gain
and adequacy of gestational weight gain in relation to guidelines (adequacy ratio) based on gestational age at delivery) are commonly used, despite their limitations, because of the constraints of the available data. Restricting analyses to term births might minimize bias, but not eliminate it (22), and would not allow the assessment of SGA and LGA outcomes. In this study, no correlation between weight gain and gestational age was found which may be because we restricted analyses to an obese population where traditional associations may not hold. In addition, where appropriate, adjustments for gestational age were made to account for the relationship between weight gain and gestational age; however, it is possible that gestational age lies in the causal pathway between weight gain and certain outcomes. Analyses were restricted to term births to avoid some of the potential bias introduced by controlled for gestational age, and the results from these models were very similar to the models that adjusted for gestational age with the exception of gestational hypertension. In this specific instance, gestational hypertension may be more dependent on other factors (i.e., fluid retention) that influence weight gain and would be difficult to separate from weight gain. This study was subject to some additional limitations. First, the data come from an older cohort when maternal pre-pregnancy obesity was less common. However, this study was restricted to obese women who made up almost 3,000 pregnancies in this cohort, and associations between pre-pregnancy BMI and outcomes have been shown to be modified by gestational weight gain since the 1970s (27), indicating that the biologic mechanisms underlying these associations are unlikely to have changed over time. In addition, as
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previously noted, results were similar to those based on more recent data with higher rates of maternal obesity. Because the pre-pregnancy weight data was based on self-report, which is prone to underestimation particularly among overweight and obese women (28), this lapse may have led to an overestimation of gain and misclassification of weight gain adequacy. Nonetheless, weight before delivery was based on measured data and because results were similar to other studies, the potential bias that could have been introduced from self-reported pre-pregnancy weight was likely minimal. There existed limited information in this data set with respect to preexisting conditions (i.e., hypertension or diabetes) that may influence weight gain. In addition, although medical advice on weight gain was different during the time of this study, associations with outcomes are not likely impacted by provision of advice. Also, while we could not separately analyze the women who lost weight from those who gained an inadequate but positive number of kilograms because of inadequate sample size, our analyses include this important group of women which adds to the value of our results. Finally, the sample size in this study was not large enough to look at more narrow categories of weight gain or loss; however, we examined weight gain as a continuous variable to maximize statistical power, and this examination is a strength. This study offers several strengths. First, the cohort contained a large number of women who gained weight below the current guidelines, compared with what might be observed today. Second, although the study was not designed to be nationally representative, it covered 12 U.S. sites and included a large sample size, allowing the inclusion of several maternal sociodemographic controls (smoking habits, socioeconomic status, and educational attainment). A large sample size of minority participants allowed for stratifications by race. Finally, the recommendations were based on a limited number of maternal and infant outcomes. This study included maternal (preeclampsia, gestational hypertension, bleeding) and infant (Apgar, breech presentation) outcomes beyond those included in the committee report, offering additional data to examine risks/benefits of inadequate weight gain in obese mothers. In this study, we found that weight gain less than the current recommendations resulted in lowered risks for LGA, preeclampsia, and gestational hypertension. However, for SGA, inadequate weight gain resulted in higher risks for class I but not class II/III obese women. Although the 2009 guidelines recommend that preconceptionally obese women should receive counseling to improve diet quality, increase physical activity, and normalize weight, the reality is that achieving normal weight before pregnancy may not be possible. Modifying gestational weight gain may
modify the baseline risks posed by high BMI. Although randomized controlled trials would help identify interventions among women with pre-pregnancy obesity that achieve the healthiest possible outcomes for themselves and their infants (29), such trials need to accumulate support from observational studies such as this one to design evidence-based trials and to inform clinical guidelines.
Acknowledgments We thank the women and girls who participated in the original Collaborative Perinatal Project and the many individuals involved in study design and data collection. We also thank Swati Bhanja (summer volunteer) and Ashlea Braun (research assistant) for their editorial contributions to the manuscript.
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22. Hutcheon JA, Bodnar LM, Joseph KS, et al The bias in current measures of gestational weight gain. Paediatr Perinat Epidemiol 2012;26(2):109–116. 23. Nohr EA, Vaeth M, Baker JL, et al Combined associations of prepregnancy body mass index and gestational weight gain with the outcome of pregnancy. Am J Clin Nutr 2008;87(6):1750– 1759. 24. Hinkle SN, Sharma AJ, Dietz PM. Gestational weight gain in obese mothers and associations with fetal growth. Am J Clin Nutr 2010;92(3):644–651. 25. Bianco AT, Smilen SW, Davis Y, et al Pregnancy outcome and weight gain recommendations for the morbidly obese woman. Obstet Gynecol 1998;91(1):97–102. 26. Artal R, Lockwood CJ, Brown HL. Weight gain recommendations in pregnancy and the obesity epidemic. Obstet Gynecol 2010;115(1):152–155. 27. Naeye RL. Weight gain and the outcome of pregnancy. Am J Obstet Gynecol 1979;135(1):3–9. 28. Mandujano A, Huston-Presley L, Waters TP, Catalano PM. Women’s reported weight: is there a discrepancy? J Matern Fetal Neonatal Med 2012;25(8):1395–1398. 29. Bodnar LM, Siega-Riz AM, Simhan HN, et al Severe obesity, gestational weight gain, and adverse birth outcomes. Am J Clin Nutr 2010;91(6):1642–1648.
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Should Obese Women Gain Less Weight in Pregnancy Than Recommended? Reena Oza-Frank, PhD, RD, and Sarah A. Keim, PhD ABSTRACT: Background: Previous research on inadequate gestational weight gain among obese women and adverse outcomes has been mixed. The objective of this study was to examine associations between inadequate gain among obese women and antepartum, intrapartum, and infant outcomes. Methods: Obese women from the U.S. Collaborative Perinatal Project were divided into obesity classes I (30.0–34.9 kg/m2) and II/III (> 35.0 kg/ m2) and three weight gain categories (inadequate: < 5 kg, adequate: 5–9 kg, excessive: > 9 kg) as defined by the U.S. Institute of Medicine. Associations between 1-kg increments of inadequate gain (< 5 kg) and outcomes were examined. Women with inadequate gain were also compared with women gaining normal (5–9 kg) and excessive (> 9 kg) weight. Results: Each fewer 1-kg of weight gain increased small-for-gestational age (SGA) risk and reduced large-for-gestational age (LGA) risk by similar magnitude. Compared with excessive gain, inadequate gain reduced the odds of preeclampsia (OR: 0.56, CI: 0.37, 0.84), gestational hypertension (OR: 0.66, CI: 0.47, 0.92), and LGA (OR: 0.48, CI: 0.38, 060) and increased the odds of SGA (OR: 2.26, CI: 1.52, 3.35). Inadequate gain offered fewer advantages over adequate weight gain: lower odds of LGA (OR: 0.75, CI: 0.57, 0.99); increased odds of SGA (OR: 1.86, CI: 1.18, 2.91). Most associations applied to obesity class I but not class II/III women. Conclusions: Inadequate weight gain poses benefits and risks to mothers and infants, but is preferable to excessive gain. The risks and benefits apply differently to class I versus class II/III obese women, indicating the need for weight gain recommendations by obesity class. (BIRTH 40:2 June 2013)
Key words: Collaborative Perinatal Project, gestational weight gain, infant, obesity, prepregnancy body mass index
Obesity among women of reproductive age in the United States (12–44 years) has increased twofold in the past 30 years, with a current prevalence of nearly 33 percent (1). Women with pre-pregnancy obesity are at increased risk of adverse pregnancy outcomes such as hypertension, preeclampsia, gestational diabetes, more frequent cesarean delivery, delivery of large-for-gestational age (LGA) infants, and stillbirths (2–7). These risks are compounded by excessive gestational weight gain (8), and optimizing weight gain may aid in reducing the risk of adverse outcomes.
In 2009, the United States Institute of Medicine released new recommendations for weight gain during pregnancy (9). Compared with the 1990 guidelines (10), the new recommendations provide an upper weight gain limit for obese women (5–9 kg). Weight gain below 5 kg is considered inadequate, and gain above 9 kg is considered excessive. This recommendation was based on limited available data considering six outcomes: small-for-gestational age (SGA), LGA, caesarean delivery, preterm delivery, postpartum weight retention, and child obesity. These data were primarily
Reena Oza-Frank and Sarah A. Keim are Principal Investigators at the Research Institute at Nationwide Children’s Hospital, Columbus, and Assistant Professors in the Department of Pediatrics, The Ohio State University, Columbus, OH, USA.
Hospital, Department of Pediatrics, The Ohio State University, 700 Children’s Drive, Research Building 3, Columbus, OH 43205, USA.
Address correspondence to Reena Oza-Frank, PhD, RD, Center for Perinatal Research, Research Institute at Nationwide Children’s
© 2013, Copyright the Authors Journal compilation © 2013, Wiley Periodicals, Inc.
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108 from women with body mass index (BMI) values of 30–34.9 kg/m2 (9), and therefore, the committee felt there existed insufficient evidence to provide guidance for women with class II (35–39.9 kg/m2) or class III (40 or more kg/m2) obesity. In addition, weight loss or weight maintenance during pregnancy was not recommended by the committee, regardless of obesity class, because of concern that low weight gains or weight loss would lead to small size at birth and poor neurologic outcomes in the offspring (11). However, it has been reported that although 50–60 percent of overweight and obese women gain more than is recommended, the prevalence of weight loss appears to increase with increasing pre-pregnancy obesity (12). A few recent studies suggest that weight gain of < 5 kg is not associated with deleterious consequences in obese mothers (8,13) and results in lowered risks of some adverse obstetric and neonatal outcomes (14,15). It is important to note that how body size and weight gain are measured and statistical analysis techniques may affect study results. Few studies have examined gestational weight gain as a continuous variable, and this lapse may obscure subtle differences across the range of weight gain values. Also, some obstetric outcomes were not examined by the committee. Therefore, the objective of this study was to examine associations between inadequate weight gain among obese women, including by obesity class and race, and a range of antepartum, intrapartum, and infant outcomes based on data from the prospective U.S. Collaborative Perinatal Project.
Materials and Methods The data are from a large prospective study, which enrolled a diverse sample of women (55,000 pregnancies) at the first prenatal visit at 12 urban U.S. sites, during 1959 to 1965 and followed women and their children to age 8 years (16). This analysis was restricted to women with a pre-pregnancy BMI 30 kg/m2 (n = 5,076), excluding pregnancies with twin or other higher order multiples (n = 254), women without a recorded race or had a race that was not black or white (477; 21 women were missing race and also carrying multiples) and women who were not weighed within 3 weeks of delivery (1,577), leaving 2,789 in the final analytical sample. Maternal pre-pregnancy BMI was calculated using self-reported pre-pregnancy weight at the first prenatal visit and measured height in inches without shoes. Pre-pregnancy BMI was categorized as obesity class I (30.0–34.9 kg/m2), class II (35.0–39.9 kg/m2), or class III ( 40.0 kg/m2). Class II (n = 588) and III (n = 233) categories were combined due to small sample sizes. Weight was measured at each prenatal visit in
street clothes without shoes or a coat. Gestational weight gain, measured both as a continuous and a categorical variable, was the main exposure. Recognizing that there exists no best measure of weight gain during pregnancy (17), weight gain was calculated as measured weight at the last prenatal visit within three weeks of delivery minus pre-pregnancy weight. For gestational weight gain categories, the current Institute of Medicine guidelines were followed, which classify obese women as inadequate (< 5 kg), adequate (5–9 kg), or excess (> 9 kg) gainers according to pre-pregnancy BMI (9). Outcomes observed were risk factors and diseases that have previously been associated with excessive or inadequate weight gain in women of varying adiposity. Maternal outcomes examined included preeclampsia (signified by both hypertension and either proteinuria or one of the following: pulmonary edema, oliguria, or convulsions from 24 weeks’ gestation to 2 weeks postpartum (18)), gestational hypertension (diastolic pressure of 90 mmHg, with onset between 24 weeks’ gestation and 2 weeks postpartum (18)), intrapartum bleeding (> 500 mL), anemia (any single value < 10 g hemoglobin or < 30% hematocrit), and breech presentation. Infant outcomes examined included SGA (birthweight in the 10th percentile or below for race and gender based on the distribution within the cohort for births at > 30 weeks’ gestation) and LGA (birthweight in the 90th percentile, as for SGA) (19). Information on gestational age, calculated on the basis of the last menstrual period, birthweight, and child’s sex was collected from the study obstetric records. Low Apgar score was also included (score < 7 at 5 minutes after birth (20)). Potential covariates identified a priori from other studies are listed in Table 1. For each pregnancy, these data were collected at the first prenatal visit interview. In the regression models, maternal age, education, socioeconomic status (21), and smoking habits (number of cigarettes smoked per day as of the first prenatal visit) were included as continuous variables.
Statistical Analysis To examine the association between weight gain and pregnancy outcomes of interest, generalized estimating equations (GEE) models were used to adjust standard errors for the clustering in the sample because of inclusion of women with more than pregnancy (n = 284). After adjusting for potential confounders, beta coefficients or odds ratios (ORs, unadjusted and adjusted) and 95 percent confidence intervals (CI), were estimated. Because gestational weight gain is likely to be correlated with gestational age at birth (22), the correlation between weight gain and gestational age was examined and gestational age was tested as a confounder in all models
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(except for SGA, LGA models). Finally, overall analyses were restricted to term births (22) to compare with results from models that included all births. Statistical
significance was based on p 0.05. Associations between inadequate weight gain and maternal and infant outcomes were examined using weight gain as a contin-
Table 1. Characteristics of Obese Women According to Categories of Gestational Weight Gain Established by the U.S. Institute of Medicine, Collaborative Perinatal Project, 1959 to 1965
Gestational Weight Gain (kg)
Maternal age (years)* 500 mL Anemia Child outcomes Small for gestational age Large for gestational age Apgar < 7 (5 minutes) Breech presentation
Stratified by Obesity Class
All Women
Black Women
White Women
Class I
Class II or III
0.97 (0.91, 1.04) 0.99 (0.95, 1.03)
0.97 (0.90, 1.05) 0.96 (0.90, 1.02)
0.97 (0.87, 1.08) 1.01 (0.94, 1.08)
0.97 (0.85, 1.10) 1.01 (0.94, 1.08)
0.97 (0.90, 1.05) 0.99 (0.93, 1.05)
0.93 (0.86, 1.00) 1.01 (0.98, 1.04)
0.94 (0.85, 1.04) 1.03 (0.99, 1.07)
0.91 (0.80, 1.03) 0.92 (0.85, 0.99)
0.94 (0.82, 1.08) 1.01 (0.96, 1.06)
0.94 (0.86, 1.02) 1.00 (0.96, 1.04)
1.06 (1.02, 1.10)
1.03 (0.98, 1.08)
1.13 (1.06, 1.21)
1.11 (1.04, 1.17)
1.02 (0.96, 1.08)
0.94 (0.90, 0.98)
0.94 (0.89, 0.99)
0.94 (0.89, 1.00)
0.82 (0.74, 0.90)
1.00 (0.96, 1.04)
0.96 (0.91, 1.01)
—
1.00 (0.93, 1.07)
0.98 (0.89, 1.07)
1.00 (0.94, 1.06)
0.99 (0.93, 1.06)
0.96 (0.85, 1.07)
1.01 (0.92, 1.11)
0.99 (0.81, 1.20)
1.00 (0.93, 1.07)
Models included: infant sex, socioeconomic status, maternal age, maternal education, number of cigarettes smoked per day, parity, gestational age (except SGA, LGA models), race (except models stratified by race), maternal pre-pregnancy BMI (except models stratified by obesity class). — denotes inadequate sample sizes to run GEE models.
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gain compared with class I obese women with adequate weight gain (0.28 [0.10–0.79]) and a lower risk of gestational hypertension (0.57 [0.34–0.94]).
Compared with women with excessive weight gain, women with inadequate weight gain were less likely to have preeclampsia (0.56 [0.37–0.84]), gestational hypertension (0.66 [0.47–0.92]), an LGA infant (0.48 [0.38–0.60]) and more likely to have an SGA infant (2.26 [1.52–3.35]) (Table 3). However, results for gestational hypertension were no longer significant when restricting to term births (0.70 [0.49–1.01]). Both black and white women with inadequate weight gain were less likely to have an LGA infant (0.43 [0.32–0.57] for white women) and more likely to have an SGA infant compared with their counterparts with excessive weight gain. Black women with inadequate weight gain were less likely to have preeclampsia (0.56 [0.33–0.93)], whereas white women with inadequate weight gain were less likely to have gestational hypertension (0.46 [0.25– 0.84]). Class I obese women with inadequate weight gain were less likely to have preeclampsia (0.43 [0.25–0.73]), gestational hypertension (0.55 [0.36–0.85]), or an LGA infant (0.40 [0.30–0.53]) compared with class I obese women with excessive weight gain. Class II/III obese women with inadequate weight gain were less likely to have an LGA infant (0.64 [0.43–0.95]) compared with class II/III women with excessive weight gain. Compared with women with adequate weight gain, women with inadequate weight gain were more likely to have an SGA infant (1.86 [1.18–2.91]) and less likely to have an LGA infant (0.75 [0.57–0.99]) (Table 4). The association with SGA remained similar by race; however, the association was not significant within obesity classes. For LGA, associations did not differ by race or obesity class. Among class I obese women, there existed a lower risk of breech presentation among infants of women with inadequate weight
Discussion We found that gestational weight gain below guidelines, compared with excessive gain, was associated with an increased risk of SGA among class I obese women, but not among class II/III obese women. Inadequate weight gain was also associated with decreased risk of LGA, again when comparing inadequate to excessive weight gain. Overall, inadequate (compared with excessive) weight gain among obese women resulted in reduced risks of maternal complications such as gestational hypertension and preeclampsia. Although our results comparing inadequate to adequate weight gain were not significant for maternal complications or LGA, there existed a trend toward more favorable outcomes among women with inadequate weight gain. This study adds to the previous literature supporting the development of weight gain recommendations specific to obesity class (14,15,24). Comparable to our study, previous studies have also shown an increased risk of SGA with inadequate weight gain among obesity class I women, but not class II/III women (15,25). Other studies have shown that this relationship exists among both class I/II women, but not class III women (14,24). Despite slight differences, these studies indicate that class I obese women may need to gain slightly more weight than class II/III obese women to minimize risk of SGA. Inadequate gestational weight gain, regardless of obesity class, results in reduced risk
Table 3. Associations Between Inadequate (< 5 kg) Compared with Excessive (> 9 kg) Gestational Weight Gain and Maternal and Child Outcomes, Overall and Stratified by Obesity Class (adjusted models), Collaborative Perinatal Project, 1959 to 1965
Stratified by Race All Women Maternal outcomes Preeclampsia Gestational hypertension Bleeding > 500 mL Anemia Child outcomes Small for gestational age Large for gestational age Apgar < 7 (5 minutes) Breech presentation
Black Women
Stratified by Obesity Class
White Women
Class I
Class II or III
0.56 0.66 0.87 1.07
(0.37, (0.47, (0.56, (0.85,
0.84) 0.92) 1.37) 1.36)
0.56 0.84 0.83 1.00
(0.33, (0.56, (0.48, (0.77,
0.93) 1.25) 1.42) 1.30)
0.52 0.46 0.97 1.48
(0.26, (0.25, (0.45, (0.84,
1.02) 0.84) 2.09) 2.59)
0.43 0.55 0.82 1.09
(0.25, (0.36, (0.48, (0.83,
0.73) 0.85) 1.41) 1.43)
0.90 0.79 1.08 0.95
(0.42, (0.42, (0.50, (0.60,
1.92) 1.45) 2.35) 1.50)
2.26 0.48 0.98 0.82
(1.52, (0.38, (0.64, (0.44,
3.35) 0.60) 1.49) 1.54)
2.16 0.43 1.17 0.67
(1.34, (0.32, (0.71, (0.29,
3.48) 0.57) 1.93) 1.52)
2.54 0.56 0.54 1.17
(1.25, (0.39, (0.26, (0.41,
5.13) 0.81) 1.15) 3.29)
2.41 0.40 0.79 0.39
(1.49, (0.30, (0.47, (0.14,
3.87) 0.53) 1.33) 1.07)
1.82 0.64 1.78 1.66
(0.91, (0.43, (0.78, (0.55,
3.64) 0.95) 4.06) 5.01)
Models included: infant sex, socioeconomic status, maternal age, maternal education, number of cigarettes smoked per day, parity, gestational age (except SGA, LGA models), race (except models stratified by race), maternal pre-pregnancy BMI (except models stratified by obesity class).
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Table 4. Associations Between Inadequate (< 5 kg) Compared with Adequate (5–9 kg) Gestational Weight Gain and Maternal and Child Outcomes, Overall and Stratified by Obesity Class (adjusted models), Collaborative Perinatal Project, 1959 to 1965
Stratified by Race All Women Maternal outcomes Preeclampsia Gestational hypertension Bleeding > 500 mL Anemia Child outcomes Small for gestational age Large for gestational age Apgar < 7 (5 minutes) Breech presentation
Black Women
Stratified by Obesity Class
White Women
Class I
Class II or III
0.96 0.70 1.07 1.16
(0.56, (0.48, (0.65, (0.88,
1.65) 1.02) 1.76) 1.53)
1.09 (0.54, 2.19) 1.01 (0.61, 1.68) — 1.10 (0.80, 1.50)
0.76 0.43 3.19 1.56
(0.31, (0.24, (0.98, (0.83,
1.85) 0.77) 10.38) 2.95)
0.81 (0.40, 1.64) 0.57 (0.34, 0.94) — 1.08 (0.79, 1.48)
1.29 0.89 1.22 1.43
(0.50, (0.47, (0.45, (0.81,
3.36) 1.69) 3.32) 2.54)
1.86 0.75 0.90 0.65
(1.18, (0.57, (0.56, (0.33,
2.91) 0.99) 1.44) 1.28)
2.04 0.72 1.05 0.43
2.05 0.71 1.01 0.43
(1.16, (0.48, (0.59, (0.18,
3.59) 1.04) 1.76) 1.02)
1.55 0.81 0.69 1.05
1.65 0.74 0.71 0.28
(0.99, (0.53, (0.40, (0.10,
2.74) 1.05) 1.28) 0.79)
(1.16, (0.49, (0.60, (0.17,
3.59) 1.04) 1.84) 1.07)
(0.74, (0.53, (0.26, (0.32,
3.23) 1.24) 1.81) 3.51)
Models included: infant sex, socioeconomic status, maternal age, maternal education, number of cigarettes smoked per day, parity, gestational age (except SGA, LGA models), race (except models stratified by race), maternal pre-pregnancy BMI (except models stratified by obesity class). — denotes inadequate sample sizes to run GEE models.
for LGA (14,15). It is important to note that this group of women who gained inadequate amounts of weight included both women who lost weight and women who gained < 5 kg, so these results are not directly equivalent to weight loss, where more research is needed. In this study and in others (14,15), risk for preeclampsia was lower among obese women with inadequate weight gains. Preeclampsia is an example of a maternal outcome where pre-pregnancy BMI is a major risk factor (25). Because guidance on weight gain may not modify all preexisting risks in obese women, it is important to balance risks of weight gain for both the mother and the child (11), with the provision of individualized recommendations based on clinical judgment (26). For example, in this study, we provide support that there may be an opportunity to improve different outcomes among class I obese women compared with class II/III obese women. We detected few statistically significant differences in the odds of outcomes between black and white women. Although not statistically significant, there existed a suggestion that the odds of gestational hypertension and preeclampsia among white women who gain an inadequate amount of weight compared with those who gained an adequate amount might be even lower than reported for the cohort overall. A larger study involving a diverse sample of women could confirm and help clarify these and other potential differences by race. Determining a method to measure gestational weight gain and simultaneously account for potential correlations with gestational age at delivery is currently under discussion (22). Total gestational weight gain and other measures (i.e., average rate of gestational weight gain
and adequacy of gestational weight gain in relation to guidelines (adequacy ratio) based on gestational age at delivery) are commonly used, despite their limitations, because of the constraints of the available data. Restricting analyses to term births might minimize bias, but not eliminate it (22), and would not allow the assessment of SGA and LGA outcomes. In this study, no correlation between weight gain and gestational age was found which may be because we restricted analyses to an obese population where traditional associations may not hold. In addition, where appropriate, adjustments for gestational age were made to account for the relationship between weight gain and gestational age; however, it is possible that gestational age lies in the causal pathway between weight gain and certain outcomes. Analyses were restricted to term births to avoid some of the potential bias introduced by controlled for gestational age, and the results from these models were very similar to the models that adjusted for gestational age with the exception of gestational hypertension. In this specific instance, gestational hypertension may be more dependent on other factors (i.e., fluid retention) that influence weight gain and would be difficult to separate from weight gain. This study was subject to some additional limitations. First, the data come from an older cohort when maternal pre-pregnancy obesity was less common. However, this study was restricted to obese women who made up almost 3,000 pregnancies in this cohort, and associations between pre-pregnancy BMI and outcomes have been shown to be modified by gestational weight gain since the 1970s (27), indicating that the biologic mechanisms underlying these associations are unlikely to have changed over time. In addition, as
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previously noted, results were similar to those based on more recent data with higher rates of maternal obesity. Because the pre-pregnancy weight data was based on self-report, which is prone to underestimation particularly among overweight and obese women (28), this lapse may have led to an overestimation of gain and misclassification of weight gain adequacy. Nonetheless, weight before delivery was based on measured data and because results were similar to other studies, the potential bias that could have been introduced from self-reported pre-pregnancy weight was likely minimal. There existed limited information in this data set with respect to preexisting conditions (i.e., hypertension or diabetes) that may influence weight gain. In addition, although medical advice on weight gain was different during the time of this study, associations with outcomes are not likely impacted by provision of advice. Also, while we could not separately analyze the women who lost weight from those who gained an inadequate but positive number of kilograms because of inadequate sample size, our analyses include this important group of women which adds to the value of our results. Finally, the sample size in this study was not large enough to look at more narrow categories of weight gain or loss; however, we examined weight gain as a continuous variable to maximize statistical power, and this examination is a strength. This study offers several strengths. First, the cohort contained a large number of women who gained weight below the current guidelines, compared with what might be observed today. Second, although the study was not designed to be nationally representative, it covered 12 U.S. sites and included a large sample size, allowing the inclusion of several maternal sociodemographic controls (smoking habits, socioeconomic status, and educational attainment). A large sample size of minority participants allowed for stratifications by race. Finally, the recommendations were based on a limited number of maternal and infant outcomes. This study included maternal (preeclampsia, gestational hypertension, bleeding) and infant (Apgar, breech presentation) outcomes beyond those included in the committee report, offering additional data to examine risks/benefits of inadequate weight gain in obese mothers. In this study, we found that weight gain less than the current recommendations resulted in lowered risks for LGA, preeclampsia, and gestational hypertension. However, for SGA, inadequate weight gain resulted in higher risks for class I but not class II/III obese women. Although the 2009 guidelines recommend that preconceptionally obese women should receive counseling to improve diet quality, increase physical activity, and normalize weight, the reality is that achieving normal weight before pregnancy may not be possible. Modifying gestational weight gain may
modify the baseline risks posed by high BMI. Although randomized controlled trials would help identify interventions among women with pre-pregnancy obesity that achieve the healthiest possible outcomes for themselves and their infants (29), such trials need to accumulate support from observational studies such as this one to design evidence-based trials and to inform clinical guidelines.
Acknowledgments We thank the women and girls who participated in the original Collaborative Perinatal Project and the many individuals involved in study design and data collection. We also thank Swati Bhanja (summer volunteer) and Ashlea Braun (research assistant) for their editorial contributions to the manuscript.
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22. Hutcheon JA, Bodnar LM, Joseph KS, et al The bias in current measures of gestational weight gain. Paediatr Perinat Epidemiol 2012;26(2):109–116. 23. Nohr EA, Vaeth M, Baker JL, et al Combined associations of prepregnancy body mass index and gestational weight gain with the outcome of pregnancy. Am J Clin Nutr 2008;87(6):1750– 1759. 24. Hinkle SN, Sharma AJ, Dietz PM. Gestational weight gain in obese mothers and associations with fetal growth. Am J Clin Nutr 2010;92(3):644–651. 25. Bianco AT, Smilen SW, Davis Y, et al Pregnancy outcome and weight gain recommendations for the morbidly obese woman. Obstet Gynecol 1998;91(1):97–102. 26. Artal R, Lockwood CJ, Brown HL. Weight gain recommendations in pregnancy and the obesity epidemic. Obstet Gynecol 2010;115(1):152–155. 27. Naeye RL. Weight gain and the outcome of pregnancy. Am J Obstet Gynecol 1979;135(1):3–9. 28. Mandujano A, Huston-Presley L, Waters TP, Catalano PM. Women’s reported weight: is there a discrepancy? J Matern Fetal Neonatal Med 2012;25(8):1395–1398. 29. Bodnar LM, Siega-Riz AM, Simhan HN, et al Severe obesity, gestational weight gain, and adverse birth outcomes. Am J Clin Nutr 2010;91(6):1642–1648.
