Objective: To compare outcomes in women with prior cesareans delivering at or before 40 weeks' gestation with those delivering after 40 weeks.
Methods: We reviewed labor outcomes over 12 years at one institution for women with one prior cesarean and no other deliveries who had a trial of labor at term. We analyzed the rates of symptomatic uterine rupture and cesarean for term deliveries before or after 40 weeks and stratified for spontaneous and induced labor. Potential confounding by birth weight was controlled using logistic regression. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated.
Results: Of 2775 women with one prior scar and no other deliveries, 1504 delivered at or before 40 weeks and 1271 delivered after 40 weeks. For spontaneous labor, rupture rate at or before 40 weeks was 0.5% compared with 1.0% after 40 weeks (P =.2, adjusted OR 2.1, CI 0.7, 5.7). For induced labor, uterine rupture rates were 2.1% at or before 40 weeks and 2.6% after 40 weeks (P =.7, adjusted OR 1.1, CI 0.4, 3.4). For spontaneous labor, rate of cesareans during subsequent trials of labor at or before 40 weeks was 25% compared with 33.5% after 40 weeks (P =.001, adjusted OR 1.5, CI 1.2, 1.8). For induced labor, rate of cesareans during subsequent trials of labor at or before 40 weeks was 33.8% compared with 43% after 40 weeks (P =.03, adjusted OR 1.5, CI 1.1, 2.2).
Conclusion: The risk of uterine rupture does not increase substantially after 40 weeks but is increased with induction of labor regardless of gestational age. Because spontaneous labor after 40 weeks is associated with a cesarean rate similar to that following induced labor before 40 weeks, awaiting spontaneous labor after 40 weeks does not decrease the likelihood of successful vaginal delivery.