Associations of maternal gestational weight gain with offspring birth size
Birth size has been associated with lifelong health and disease risk. Better understanding of modifiable risk factors for birth size will help identify at-risk pregnancies and intervention targets. Effects of gestational weight gain (GWG) during specific periods of pregnancy and potential effect modification by offspring gender or maternal pre-pregnancy leisure-time physical activity (LTPA) remain largely unknown.
We conducted a prospective cohort study of 3,624 mothers and their singleton offspring who sought prenatal care at clinics affiliated with Swedish Medical Center and Tacoma General Hospital, Seattle and Tacoma, WA, 1996-2008. Information on socio-demographic characteristics and medical history was obtained by questionnaire at an average of 15 weeks gestation. GWG (kg) and birth size measures (BSM) including birthweight (BW; g), ponderal index (PI; g/cm3*100), crown-heel length (CHL; cm), and head circumference (HC; cm) were abstracted from medical records. GWG was characterized as total, early (<20 weeks), and late (≥20 weeks) GWG. "Moderate to vigorous physical activity" was defined as average weekly minutes spent in activity at a metabolic equivalent rating ≥6.We used multivariable linear regression to calculate mean differences and 95% CIs relating total, early, and late GWG to BSM. We tested whether associations of early GWG and late GWG with birth size were quantitatively different using Wald tests. We also tested whether the associations differed by offspring sex or maternal pre-pregnancy LTPA using stratified analyses and interaction terms.
Average total, early, and late GWG were 16.2, 6.8, and 9.5 kg, respectively. We found strong positive associations of total GWG, early GWG, and late GWG with BW. A 1kg increase in total GWG was associated with a 17.2g increase in BW (95% CI 13.8-18.9). A 1kg increase in early GWG was associated with a 14.1g increase (95% CI 10.3-18.0) in BW after adjustment for late GWG. A 1kg increase in late GWG was associated with a 21.0g increase in BW (95% CI 16.7-25.4) after adjustment for early GWG. The association differed for early vs. late GWG (p=0.026). Sex-stratified results for total GWG-BW associations were similar to overall results, but there were sex-specific quantitative differences in early and late GWG-BW associations. Among males, early GWG-BW and late GWG-BW associations were similar (early 15.7, 95% CI 10.0-21.4; late 18.2, 95% CI 12.0-24.5; comparison p=0.579). Among females, a 1kg increase in early GWG was associated with a 12.0g increase in BW (95% CI 6.7-17.2), while a 1kg increase in late GWG was associated with a 24.2g increase in BW (95% CI 18.2-30.3) and these differences were statistically significant (p=0.0042). Sex-GWG (both early and late) interaction terms were not significant however (p=0.549 and 0.354, respectively). Total, early, and late GWG were associated with CHL and HC, but not with PI. There was no evidence that these associations differed by early or late GWG, and the observed associations were not present after adjustment for BW. There was no effect modification of associations of GWG with any of the BSM by LTPA.
Fetuses, particularly female fetuses tend to gain more weight with higher levels of late GWG than with similar higher levels of early GWG. Investigators should consider both period- and sex-specific differences in GWG-BW associations when planning, executing, and interpreting observational and interventional studies.