Maternal Physical Activity at Term and Spontaneous Labor: A Case-Crossover Study

Background: This study assessed associations between antenatal physical activity and the onset of spontaneous labor (SL). Methods: Data were taken from 541 participants in the third pregnancy, infection, and nutrition study who had no contra-indications to antenatal physical activity. An interviewer-administered questionnaire assessed labor triggers, gestational age at birth, and physical activity within the week (24 h to 7 d) and the 24-hour period (0-24 h) prior to SL. A case-crossover design examined the association between physical activity (recreational, occupational, or any) and the risk of onset of SL within the subsequent 24 hours. Results: Overall, 21% (any), 26% (recreational), and 14% (occupational) of participants reported physical activity during the week; whereas 5% (any), 7% (recreational), and 3% (occupational) reported physical activity during the 24-hour period, prior to SL onset. Participants who reported any or occupational physical activity during the 24-hour period had a decreased likelihood of SL within the subsequent 24 hours, while participants who reported at least 30 minutes of recreational physical activity had an increased likelihood. Results remained consistent among early, full, or postterm participants. Conclusion: Recreational, but not occupational, physical activity at term may increase the likelihood of SL; however, the authors cannot rule out reverse causality.