Exercise during pregnancy and risk of cesarean delivery in nulliparous women: a large population-based cohort study

BACKGROUND: Vaginal delivery for the first birth is of great importance for further obstetric performance for the individual woman. Given the rising cesarean delivery rates worldwide over the past decades, a search for modifiable factors that are associated with cesarean delivery is needed. Exercise may be a modifiable factor that is associated with type of delivery, but the results of previous studies are not conclusive. OBJECTIVE: The purpose of this study was to investigate the association between exercise during pregnancy and cesarean delivery, both acute and elective, in nulliparous women. STUDY DESIGN: We conducted a population-based cohort study that involved 39,187 nulliparous women with a singleton pregnancy who were enrolled in the Norwegian Mother and Child Cohort Study between 2000 and 2009. All women answered 2 questionnaires in pregnancy weeks 17 and 30. Acute and elective cesarean delivery data were obtained from the Medical Birth Registry of Norway. Information on exercise frequency and type was assessed prospectively by questionnaires in pregnancy weeks 17 and 30. Generalized linear models estimated risk differences of acute and elective cesarean delivery for different frequencies and types of exercise during pregnancy weeks 17 and 30. We used restricted cubic splines to examine dose-response associations of exercise frequency and acute cesarean delivery. A test for nonlinearity was also conducted. RESULTS: The total cesarean delivery rate was 15.4% (n = 6030), of which 77.8% (n = 4689) was acute cesarean delivery. Exercise during pregnancy was associated with a reduced risk of cesarean delivery, particularly for acute cesarean delivery. A nonlinear association was observed for exercise frequency in weeks 17 and 30 and risk of acute cesarean delivery (test for nonlinearity, P = .003 and P = .027, respectively). The largest risk reduction was observed for acute cesarean delivery among women who exercised>5 times weekly during weeks 17 (-2.2%) and 30 (-3.6%) compared with nonexercisers (test for trend, P<.001). Reporting high impact exercises in weeks 17 and 30 was associated with the greatest reduction in risk of acute cesarean delivery (-3.0% and -3.4%, respectively). CONCLUSION: Compared with nonexercisers, regular exercise and high-impact exercises during pregnancy are associated with reduced risk of having an acute cesarean delivery in first-time mothers.