Effect of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor.

OBJECTIVE: We examined the effect of prior vaginal delivery on the risk of uterine rupture in pregnant women undergoing a trial of labor after prior cesarean delivery.

STUDY DESIGN: The medical records of all pregnant women with a history of cesarean delivery who attempted a trial of labor during a 12-year period at a single center were reviewed. For the current analysis, the study population was limited to term pregnancies. The effect of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor was evaluated. Separate analyses were performed for women with a single previous cesarean delivery and for those with >1 prior cesarean delivery. For each of these subgroups, the rate of uterine rupture among women who had > or =1 prior vaginal delivery was compared with the rate among women with no prior vaginal delivery. Logistic regression analysis was used to examine the associations with control for confounding factors.

RESULTS: Of 3783 women with 1 prior scar, 1021 (27.0%) also had > or =1 prior vaginal delivery. During a subsequent trial of labor, the rate of uterine rupture was 1.1% among pregnant women without prior vaginal delivery and 0.2% among pregnant women with prior vaginal delivery (P =.01). Logistic regression analysis controlling for duration of labor, induction, birth weight, maternal age, year of birth, epidural analgesia, and oxytocin augmentation indicated that, among women with a single scar, those with a prior vaginal delivery had a risk of uterine rupture that was one fifth that of women without a previous vaginal delivery (odds ratio, 0.2; 95% confidence interval, 0.04-0.8). In the group of 143 pregnant women with >1 previous cesarean delivery, women with a prior vaginal delivery had a somewhat lower risk of uterine rupture (3.9% vs 2.5%; adjusted odds ratio, 0.6; 95% confidence interval, 0.01-6.7). This difference was not statistically significant.

CONCLUSION: Among women with 1 prior cesarean delivery undergoing a subsequent trial of labor, those with a prior vaginal delivery were at substantially lower risk of uterine rupture than women without a previous vaginal delivery.