Maternal and obstetric complications of pregnancy are associated with increasing gestational age at term.

OBJECTIVE: We sought to estimate when rates of maternal pregnancy complications increase beyond 37 weeks of gestation.

STUDY DESIGN: We designed a retrospective cohort study of all low-risk women delivered beyond 37 weeks' gestational age from 1995 to 1999 within a mature managed care organization. Rates of mode of delivery and maternal complications of labor and delivery were examined by gestational age with both bivariate and multivariable analyses.

RESULTS: We found that, among the 119,254 women who delivered at 37 completed weeks and beyond, the rates of operative vaginal delivery (OR 1.15, 95% CI 1.09, 1.22), 3rd- or 4th-degree perineal laceration (OR 1.15, 95% CI 1.06, 1.24), and chorioamnionitis (OR 1.32, 95% CI 1.21, 1.44) all increased at 40 weeks as compared to 39 weeks of gestation (P < .001), and rates of postpartum hemorrhage (OR 1.21, 95% CI (1.10, 1.32), endomyometritis (OR 1.46, 95% CI 1.14, 1.87), and primary cesarean delivery (1.28, 95% CI 1.20, 1.36) increased at 41 weeks of gestation (P < .001). The cesarean indications of nonreassuring fetal heart rate (OR 1.81, 95% CI 1.49, 2.19) and cephalo-pelvic disproportion (OR 1.64, 95% CI 1.40, 1.94) increased at 40 weeks of gestation (P < .001).

CONCLUSION: We found that the risk of maternal peripartum complications increase as pregnancy progresses beyond 40 weeks of gestation. Management of pregnancies that progress past their EDC should include counseling regarding the risks of increasing gestational age.