Factors correlated with physical activity during pregnancy and associations of physical activity with spontaneous abortion, length of gestation, and birthweight

The first study aim was to identify characteristics associated with self-reported physical activity at 17-22 and 27-30 weeks gestation using data from the Pregnancy, Infection, and Nutrition 3 Study. Correlates of low level recreational activity were mostly sociodemographic but most sociodemographics were not also correlated with higher level recreational activity. At 27-30 weeks, overweight/obese women were less likely to engage in recreational activity. At 17-22 weeks, women who began prenatal care later and women with a history of miscarriage were less likely to engage in recreational activity. Physical activity was positively associated with partner support and enjoyment of physical activity. This analysis is limited by self-reported physical activity measures and the performance of model selection based on a p-value. These associations may help target interventions to increase activity during pregnancy.;The second aim was to examine the association between vigorous physical activity and gestational age and birthweight (among term births). The third aim was to examine the association between vigorous physical activity and spontaneous abortion. Both aims used data from the Right From the Start Study, which measured vigorous physical activity at 13-16 weeks gestation. The association of total vigorous physical activity with preterm birth was U-shaped. However, vigorous recreational activity was associated with lower odds of preterm birth. Performing at least five sessions of vigorous recreational activity per week was associated with decreased odds of earlier birth (odds ratio (OR) (95% confidence interval, (CI)): 0.66 (0.36, 1.21)). Women who reported starting exercise in preparation for pregnancy had lower odds of earlier birth OR(CI): 0.65 (0.45, 0.94), none gave birth preterm. Women who reported decreasing their vigorous activity from pre-pregnancy to interview had lower odds of spontaneous abortion, OR(CI): 0.44 (0.32, 0.61). We found no evidence that vigorous recreational activity was associated with adverse changes in pregnancy outcome. These analyses are limited by self-reported activity measures and low prevalence of vigorous activity. The spontaneous abortion analysis is susceptible to recall bias. Our analysis suggests that vigorous recreational activity during pregnancy may be safe. Future studies should examine the association of vigorous recreational activity with maternal injury and other perinatal outcomes.