Association Between Physical Activity and the Onset of Spontaneous Labor

PURPOSE: To determine whether prenatal physical activity (any, recreational, or occupational) the week before delivery was associated with increased risk of spontaneous labor (SL) onset. METHODS: We used data from 541 women participating in the third Pregnancy, Infection, and Nutrition Study (PIN3) who reported SL onset and for whom antenatal physical activity was not contraindicated. An interviewer-administered questionnaire measured labor triggers, gestational age at birth, and physical activity (frequency, duration, and intensity) performed both within the week and 24-hour period prior to labor onset. A self-matched, case-crossover design examined the association between activity in the 0 to 24 hours preceding SL onset compared to the week (24 hours to 7 days) before onset of labor. RESULTS: Among these women who experienced SL, 92% (any), 57% (recreational), and 25% (occupational) reported performing physical activity during the week before their labor began, whereas 71% (any), 33% (recreational), and 9% (occupational) reported performing physical activity during the 24-hour period before their labor began. Compared with the week before their labor, the immediate odds of SL were decreased within 24 hours of performing ≤30 minutes of any physical activity [(OR30 minutes: 0.74; 95% CI: 0.74-1.00); (Figure 1)]. The immediate odds of SL were also decreased within 24 hours of ≤45 minutes of occupational physical activity (OR45 minutes: 0.39; 95% CI: 0.18-0.85). However, the immediate odds of SL were increased within 24 hours of performing ≥30 minutes of recreational physical activity (OR30 minutes: 1.54; 95% CI: 1.09-2.15). CONCLUSION: Any and occupational physical activity were associated with a decreased likelihood of SL within 24 hours, while recreational physical activity was associated with an increased likelihood of SL. Future research should assess the potential for reverse causality.