Intrapartum uterine rupture and dehiscence in patients with prior lower uterine segment vertical and transverse incisions

Objective: To determine whether gravidas with prior low vertical uterine incision(s) are at a higher risk for uterine rupture during a trial of labor after cesarean delivery than women with prior low transverse uterine incision(s). Methods: The medical records of women undergoing a trial of labor after prior cesarean delivery over a 12-year period (July 1984-June 1996) at a tertiary-care hospital were reviewed. Maternal and perinatal outcomes for women with prior low transverse and low vertical incision were compared. Women whose low vertical incision was noted to extend into the corpus of the uterus were excluded. All uterine scar disruptions, which included both symptomatic ruptures and detected asymptomatic dehiscences, were analyzed together, and ruptures were examined separately. Results: The outcomes of 2912 patients undergoing trial of labor for the low transverse group and 377 patients undergoing trial of labor for the low vertical group were compared. Overall, there were 38 (1.3%) scar disruptions in the low transverse group and six (1.6%) in the low vertical group, P = .6. There were 28 (1.0%) symptomatic ruptures in the low transverse group and 3 (0.8%) in the low vertical group, P > .999. The study had a power of 89% to detect an increase in the low vertical rupture rate from 1% (as noted for low transverse incisions) to 3%. Conclusion: Gravidas with a prior low vertical uterine incision are not at increased risk for uterine rupture during a trial of labor compared with women with a prior low transverse uterine incision. (C) 1999 by The American College of Obstetricians and Gynecologists.