Physical Activity Volumes during Pregnancy: A Systematic Review and Meta-Analysis of Observational Studies Assessing the Association with Infant's Birth Weight.

Objective This study aims to examine the association between different maternal physical activity exposures during pregnancy and infant's birth weight, body composition, and risk of inadequate weight. Methods Two reviewers (M.B. and J.L.G.) identified observational studies reporting total or leisure time activity during pregnancy and birth weight outcomes. Pooled analyses were performed to summarize the risk associated with high or moderate volumes of physical activity on birth weight. Results A total of 54 studies among 4,080 reported the association between physical activity and birth weight (37 studies) or risks of small or large birth weight. The association between physical activity and birth weight was evaluated by physical activity levels (low, moderate, or high). Despite heterogeneity, pooled results (23 studies) suggested that moderate levels of activity are associated with an increased birth weight (mean difference: 61.5 g, 95% confidence interval [CI]: 16.6, 106.5, 15 studies), while high levels were associated with lower birth weight (mean difference: -69.9 g, 95% CI: -114.8, -25.0, 15 studies). Data were insufficient to provide robust estimates for other outcomes. Conclusions The results of observational studies suggest an inverted u-shaped association between physical activity and birth weight, despite methodological variability. These results could help refining physical activity guidelines for pregnancy and provide guidance for future research.