The effect of gestational age on trial of labor after Cesarean section.

OBJECTIVES: To evaluate the effect of gestational age on the rate of successful vaginal delivery and the rate of uterine rupture in patients undergoing a trial of labor (TOL) after a prior Cesarean delivery.

STUDY DESIGN: This was a cohort study including patients with a live singleton fetus undergoing a TOL after a previous low transverse Cesarean delivery between 1988 and 2002. Patients were divided into three groups according to gestational age: 24-36 weeks 6 days, 37-40 weeks 6 days and > or = 41 weeks. Obstetric outcomes, including the rates of successful vaginal delivery and symptomatic uterine rupture, were compared between the groups. Multivariate logistic regression analysis was performed to adjust for potential confounding factors.

RESULTS: There were 253, 1911 and 329 patients in each group, respectively. In patients with advanced gestational age (> or = 41 weeks) the rate of uterine rupture was significantly higher (0% vs. 1.0% vs. 2.7%, p = 0.006) and the rate of successful vaginal deliveries was significantly lower (83% vs. 76.9% vs. 62.6%, p < 0.001). After adjusting for confounding variables, advanced gestational age was associated with a lower rate of successful vaginal delivery (odds ratio 0.68, 95% CI 0.51-0.89), and a higher rate of uterine rupture (odds ratio 2.85, 95% CI 1.27-6.42) when compared to 37-40 weeks 6 days.

CONCLUSION: Advanced gestational age is associated with higher rates of failed TOL and uterine rupture.