Physical Activity During Pregnancy and Preterm Birth: Findings From the 2015 Pelotas (Brazil) Birth Cohort Study.

Background: Physical activity (PA) during pregnancy is associated with several benefits in maternal and child outcomes, and its relationship with preterm birth is still conflicting. This study aims to examine the associations between PA during pregnancy and occurrence of preterm birth. Methods: PA was assessed by questionnaire (for each trimester) and accelerometry (second trimester) in women enrolled in a birth cohort study that started during pregnancy and included births that occurred between January 1 and December 31, 2015. Gestational age was based on the last menstrual period and ultrasonography. All deliveries before 37 weeks of gestation were considered preterm births. A Poisson regression model was used to measure associations controlling for potential confounders. Results: PA information was available for 4163 women and 13.8% of births were preterm. A total of 15.8% of women were engaged in PA during pregnancy. Multivariate analysis showed that only PA performed in the third trimester of pregnancy (prevalence ratio = 0.58; 95% confidence interval, 0.36-0.96) was associated with the outcome. Conclusions: PA performed in the third trimester of pregnancy was associated with a protection to preterm birth. Pregnant women should be counseled to engage in PA to lower the risk of premature delivery.