Leisure-time Physical Activity During Pregnancy And The Birth Weight Distribution: Where Is The Effect?

Abstract

Previous reports have shown leisure-time physical activity (LTPA) during pregnancy to be related to small decreases in mean birth weight and/or decreased risk of giving birth to a large for gestational age infant. However, the effect of LTPA across the entire birth weight distribution has not been examined. PURPOSE: To characterize the relationship between pregnancy LTPA and birth weight. METHODS: Women enrolled in the Pregnancy Outcomes and Community Health Study (1998-2004) were followed-up in 2007. Follow-up efforts were extensive for a subcohort and minimal for the remainder, or non-subcohort. As a result, 596 (67% of eligible) subcohort and 418 (26% of eligible) non-subcohort women who delivered at term were included in this investigation. Original data collection provided maternal demographics. Medical records provided child gender, gestational age, and birth weight. Gender and gestational age-specific birth weight z-scores (BWz) were calculated and offspring were categorized as small-, appropriate-, or large-for-gestational-age (SGA, AGA, and LGA, respectively). At follow-up, women recalled pregnancy LTPA and were classified as inactive, insufficiently active (> 0 but < 7.5 kcal/kg/wk), and meeting LTPA recommendations (≥ 7.5 kcal/kg/wk). Linear, logistic, and quantile regression analyses were conducted separately by subcohort status. RESULTS: The subcohort had greater racial and socioeconomic diversity than the non-subcohort. In multivariate linear regressions, LTPA was not associated with changes in mean birth weight among either group. Among the non-subcohort, meeting LTPA recommendations significantly decreased odds of LGA (aOR=0.30, 95%CI: 0.14-0.64) without affecting odds of SGA. Quantile regression analyses showed that meeting LTPA recommendations was unrelated to BWz until the 0.65 quantile, after which it significantly reduced BWz among the non-subcohort. Results for the subcohort were similar but not statistically significant. CONCLUSIONS: LPTA during pregnancy appears to lower odds of LGA and reduce BWz among the upper quantiles without causing a mean shift in the entire distribution. Due to adverse maternal and child health effects associated with high birth weight, our results may indicate a substantial health benefit for LTPA during pregnancy.