TY - JOUR
T1 - The association between pregnancy weight gain and birthweight
T2 - A within-family comparison
AU - Ludwig, David S.
AU - Currie, Janet
N1 - Funding Information:
Weight gain during pregnancy has been associated with high birthweight and measures of adiposity early in life. Our study, using a state-based registry with more than one million singleton births, provides evidence for a causal association that is independent of shared genes. We noted that every kg increase in pregnancy weight gain increases birthweight by about 7·35 g, and that variation in pregnancy weight gain through the recorded range can affect birthweight by about 200 g. Because high birthweight predicts BMI later in life, 12,14,17–19,21 these findings suggest that excessive weight gain during pregnancy could raise the long-term risk of obesity-related disease in offspring. High birthweight might also increase risk of other diseases later in life, including asthma, atopy, and cancer. 13,15,16,20 With respect to potential mechanisms, the physiological pathways that might link fetal overnutrition to high birthweight have been described. During pregnancy, insulin resistance develops in the mother to shunt vital nutrients to the growing fetus. 38 Excessive weight or weight gain during pregnancy exaggerates this normal process by further increasing insulin resistance and possibly also by affecting other maternal hormones that regulate placental nutrient transporters. 39 The resulting high rate of nutrient transfer stimulates fetal insulin secretion, overgrowth, and increased adiposity. Indeed, maternal postprandial glycaemia in the third trimester, even within the normal range, is strongly associated with birthweight. 40 The mechanisms whereby in-utero overnutrition and related physiological derangements affect bodyweight later in life remain speculative, 9,11,39 though the crucial role of maternal hyperglycaemia has been further emphasised by recent research. 41 The primary limitations of this study surround the possibility of measurement error and confounding. The pregnancy weight gain variable, more so than birthweight, is subject to recall and reporting bias that might vary by BMI, education, and level of prenatal care, among other factors. However, the within-subject design would tend to keep systematic bias arising from such factors to a minimum. Thus, some individuals might tend to underestimate and others to overestimate weight gain, although each would likely do so in a similar fashion across several pregnancies. Any random measurement error would tend to diminish apparent effect size, 42 causing our estimates to be conservative. Additionally, results of a secondary analysis excluding individuals with inadequate prenatal care—a group especially subject to error in the measurement of pregnancy weight gain—were very similar to those of the primary analysis. Other evidence of reliability derives from associations in the expected direction here (with length of pregnancy and smoking) and elsewhere (with pre-eclampsia, cephalopelvic disproportion, failed induction, and caesarean delivery) 33 involving the pregnancy weight gain variable obtained from birth certificates. Furthermore, results of a validation study showed an exact concordance between pregnancy weight gain obtained from birth certificates and from medical records 82·8% of the time. 32 Our within-subject design should effectively eliminate confounding by genetic and other unvarying factors. An important study limitation is the absence of information about maternal BMI before pregnancy. We address this limitation to some degree through the use of fixed-effects models and adjustment for age and parity, controlling in part for BMI before the first pregnancy and weight change between pregnancies. In any event, we contend that absence of prepregnancy BMI could not account for the primary findings for a fundamental statistical reason. For a confounder to account for a positive association between an independent variable and a dependent variable, it must be associated with both in the same way, either positive or inverse. But prepregnancy BMI is inversely associated with pregnancy weight gain, 43–45 and positively associated with birthweight. 22–26 Additionally, we used a secondary analytical approach to examine for residual confounding, comparing differences in subsequent pregnancies for each mother ( figure 2B ). We found that weight gain had a similar effect on birthweight irrespective of which pregnancy had greatest weight gain. This effect would not have occurred if prepregnancy BMI had differed between pregnancies in a systematic way that confounded the findings. We recognise that pregnancy weight gain might affect birthweight differently in women with high compared with low prepregnancy BMI (ie, effect modification). However, the similarity in findings from analyses of subgroups expected to differ in prepregnancy BMI, such as older and younger women or black and white women, provides evidence against this possibility (and against confounding). Moreover, unrecognised effect modification by prepregnancy BMI, diet quality, level of physical activity, or other factors would not threaten the validity of our primary findings. Several other methodological issues merit consideration. Concern about reverse causation can largely be dismissed, because increased fetal weight would make a small contribution (<10%) to the associated increase in maternal weight. Even so, we cannot rule out the possibility that hormonal or metabolic signals from the fetus might have an additional effect on maternal weight. Some women with unrecognised diabetes might have been present in our sample and have contributed to the observed effect size, especially if they developed the disease in some but not all of their pregnancies. Furthermore, diagnostic criteria and screening practices might have changed during the study. We aimed to minimise these effects by excluding individuals who reported diabetes during any pregnancy, a group that would be at highest risk during every pregnancy. Additionally, there was no significant difference in a subgroup analysis of older women, who are at substantially increased risk for this complication. 46 Finally, we recognise the absence of information about paternity as a study limitation. However, the similar effect of maternal weight gain on birthweight in first and second pregnancies, irrespective of which had greater weight gain, argues against any systematic bias. In conclusion, our findings suggest that excessive maternal weight gain during pregnancy increases birthweight; in view of the apparent association between high birthweight and adult adiposity, pregnancy might be an advantageous time to initiate obesity prevention efforts. Contributors DSL and JC both contributed to the design of the study and drafting of the report. DSL formulated the study hypotheses and JC supervised data collection and analysis. Conflicts of interest We declare that we have no conflicts of interest. Acknowledgments Data collection for this project was supported under US National Institutes of Health grant R21 HD055613-01 . DSL was supported in part by a career grant from the National Institute of Diabetes and Digestive and Kidney Diseases ( K24 DK082730 ) and a grant from the New Balance Foundation. Cecilia Machado provided assistance with research. We thank Cara Ebbeling, Matthew Gillman, Steven Gortmaker, Joseph Majzoub, and Eric Rimm for critical review of the report.
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
PY - 2010/9/18
Y1 - 2010/9/18
N2 - Background Excessive weight gain during pregnancy seems to increase birthweight and the offspring's risk of obesity later in life. However, this association might be confounded by genetic and other shared effects. We aimed to examine the association between maternal weight gain and birthweight using state-based birth registry data that allowed us to compare several pregnancies in the same mother. Methods In this population-based cohort study, we used vital statistics natality records to examine all known births in Michigan and New Jersey, USA, between Jan 1, 1989, and Dec 31, 2003. From an initial sample of women with more than one singleton birth in the database, we made the following exclusions: gestation less than 37 weeks or 41 weeks or more; maternal diabetes; birthweight less than 500 g or more than 7000 g; and missing data for pregnancy weight gain. We examined how differences in weight gain that occurred during two or more pregnancies for each woman predicted the birthweight of her offspring, using a within-subject design to reduce confounding to a minimum. Findings Our analysis included 513 501 women and their 1 164 750 offspring. We noted a consistent association between pregnancy weight gain and birthweight (β 7·35, 95 CI 7·10-7·59, p<0·0001). Infants of women who gained more than 24 kg during pregnancy were 148·9 g (141·7-156·0) heavier at birth than were infants of women who gained 8-10 kg. The odds ratio of giving birth to an infant weighing more than 4000 g was 2·26 (2·09-2·44) for women who gained more than 24 kg during pregnancy compared with women who gained 8-10 kg. Interpretation Maternal weight gain during pregnancy increases birthweight independently of genetic factors. In view of the apparent association between birthweight and adult weight, obesity prevention efforts targeted at women during pregnancy might be beneficial for offspring. Funding US National Institutes of Health.
AB - Background Excessive weight gain during pregnancy seems to increase birthweight and the offspring's risk of obesity later in life. However, this association might be confounded by genetic and other shared effects. We aimed to examine the association between maternal weight gain and birthweight using state-based birth registry data that allowed us to compare several pregnancies in the same mother. Methods In this population-based cohort study, we used vital statistics natality records to examine all known births in Michigan and New Jersey, USA, between Jan 1, 1989, and Dec 31, 2003. From an initial sample of women with more than one singleton birth in the database, we made the following exclusions: gestation less than 37 weeks or 41 weeks or more; maternal diabetes; birthweight less than 500 g or more than 7000 g; and missing data for pregnancy weight gain. We examined how differences in weight gain that occurred during two or more pregnancies for each woman predicted the birthweight of her offspring, using a within-subject design to reduce confounding to a minimum. Findings Our analysis included 513 501 women and their 1 164 750 offspring. We noted a consistent association between pregnancy weight gain and birthweight (β 7·35, 95 CI 7·10-7·59, p<0·0001). Infants of women who gained more than 24 kg during pregnancy were 148·9 g (141·7-156·0) heavier at birth than were infants of women who gained 8-10 kg. The odds ratio of giving birth to an infant weighing more than 4000 g was 2·26 (2·09-2·44) for women who gained more than 24 kg during pregnancy compared with women who gained 8-10 kg. Interpretation Maternal weight gain during pregnancy increases birthweight independently of genetic factors. In view of the apparent association between birthweight and adult weight, obesity prevention efforts targeted at women during pregnancy might be beneficial for offspring. Funding US National Institutes of Health.
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U2 - 10.1016/S0140-6736(10)60751-9
DO - 10.1016/S0140-6736(10)60751-9
M3 - Article
C2 - 20691469
AN - SCOPUS:77956929653
SN - 0140-6736
VL - 376
SP - 984
EP - 990
JO - The Lancet
JF - The Lancet
IS - 9745
ER -