"Higher maximum doses of oxytocin are associated with an unacceptably high risk for uterine rupture in patients attempting vaginal birth after cesarean delivery". American Journal of Obstetrics and Gynecology, 199, 1, 32.e1-32.e5. 2008 Objective: To more precisely estimate the effect of maximum oxytocin dose on uterine rupture risk in patients attempting VBAC by considering timing and duration of therapy.Study design: A nested case-control study was conducted within a multicenter, retrospective cohort study of over 25,000 women with at least one prior cesarean delivery, comparing cases of uterine rupture to controls (no rupture) while attempting VBAC. Time-to-event analyses were performed to examine the effect of maximum oxytocin dose on the risk of uterine rupture considering therapy duration, while adjusting for confounders.Results: Within the nested case-control study of 804 patients, 272 were exposed to oxytocin: 62 cases of uterine rupture and 210 controls. Maximum oxytocin ranges above 20mu/min increased the risk of uterine rupture 4-fold or greater (21-30mu/min: HR=3.92, 95%CI 1.06-14.52; 31-40mu/min: HR=4.57, 95%CI 1.00-20.82).Conclusion: These findings support a maximum oxytocin dose of 20mu/min in VBAC trials to avoid an unacceptably high risk of uterine rupture.