BACKGROUND: Previous studies report conflicting results regarding a possible association between maternal physical activity (PA) and cesarean delivery. METHODS: 7-day PA recalls were collected by telephone from n=1205 pregnant women from North Carolina, without prior cesarean, during two time windows: 17-22 weeks and 27-30 weeks completed gestation. PA was treated as a continuous, non-linear variable in binomial regressions (log-link function); models controlled for primiparity, maternal contraindications to exercise, pre-eclampsia, pregravid BMI, and percent poverty. We examined both total PA and moderate-to-vigorous PA (MVPA) at each time. Outcomes data came from medical records. RESULTS: The dose-response curves between PA or MVPA and cesarean risk at 17-22 weeks followed an inverse J-shape, but at 27-30 weeks the curves reversed and were J-shaped. However, only (total) PA at 27-30 weeks was strongly associated with cesarean risk; this association was attenuated when women reporting large volumes of PA (>97.5th percentile) were excluded. CONCLUSION: We did not find evidence of an association between physical activity and cesarean birth. We did, however, find evidence that associations between PA and risk of cesarean may be non-linear and dependent on gestational age at time of exposure, limiting the accuracy of analyses that collapse maternal PA into categories.This is an author's peer-reviewed final manuscript, as accepted for publication. The published article is copyrighted by Human Kinetics, Inc., and can be found at: http://journals.humankinetics.com/jpah-back-issues/jpah-volume-12-issue-1-january/exposure-analysis-methods-impact-associations-between-maternal-physical-activity-and-cesarean-deliveryKeywords: childbirth, exposure coding, exercise, prospective, cohort stud
