Physical activity and fetal growth during pregnancy

OBJECTIVE: To assess the separate and combined relationships of aerobic physical activity during pregnancy, maternal weight gain during pregnancy, and height to the fetal growth ratio. METHODS: The aerobic physical activity of 51 healthy, nonsmoking pregnant women was assessed for 48 hours at both 20 and 32 weeks of pregnancy by accelerometry, heart rate monitoring, and physical activity recall. We analyzed the relationship between maternal physical activity and the fetal growth ratio. RESULTS: All women included in the analysis completed healthy, uncomplicated pregnancies and delivered infants with a weight range of 2,743-4,943 g. Aerobic physical activity assessed by accelerometry was strongly and inversely associated with fetal growth ratio (r=-0.42; P <.002). Infants born to women in the highest quartile of physical activity weighed 608 g less than infants born to women in the lowest quartile. The inverse relationship between physical activity and fetal growth ratio was moderated by maternal height; virtually all the effect was seen in mothers taller than the sample median (1.65 m). Similar relationships were found across methods of physical activity measurement. CONCLUSION: Aerobic physical activity in pregnancy may be an important determinant of birth weight within the normal range, especially in taller mothers.