of a trial of labor compared with an elective repeat cesarean delivery after a previous cesarean in a minimally biased cohort Sharon A. Gilbert For the Eunice Kennedy Shriver National Institute of Child Health and Human Development, MaternalFetal Medicine Units Network, Bethesda, MD OBJECTIVE: To determine the most cost-effective strategy for women eligible for a trial of labor (TOL) with one prior cesarean delivery and balanced baseline characteristics. STUDY DESIGN: We developed a decision analysis model comparing TOL after one prior cesarean with an elective repeat cesarean delivery (ERCD) for a hypothetical cohort of 100,000 women with no contraindication to a TOL. To derive probability estimates, a group of women who underwent either TOL or ERCD were selected from a 1999-2002 prospective study. The final probabilistic estimates were obtained from women who underwent TOL or ERCD and were selected by propensity score analysis as being matched according to their baseline characteristics. Cost data were obtained from national databases and included hospital, obstetrician, pediatrician, and anesthesiologist costs as well as opportunity costs of the mother and a caregiver. Quality adjusted life-years (QALYs) were obtained from the literature. Probability, cost and QALY data for the outcome of cerebral palsy were obtained from the literature as well. The primary outcome was cost-effectiveness measured as the marginal cost per QALY gained, with a $50,000 threshold per QALY. RESULTS: According to baseline estimates, the TOL strategy dominated the ERCD strategy, with $142.4 million saved and 1793 QALYs gained per 100,000 women. The model was sensitive to five variables (table). Bivariable analysis on the probability of successful TOL and uterine rupture indicated when the probability of success was at the base value, 68.5%, TOL was preferred if the probability of rupture was 4.6% or less (graph). When uterine rupture was at the base value, 0.8%, TOL was preferred if the probability of successful TOL was 40.8% or more. CONCLUSION: A TOL after one prior cesarean is less expensive and more effective than an ERCD in a group of women with balanced baseline characteristics; these results are sensitive to five variables, which need to be considered in cost-effective assessment. www.AJOG.org Epidemiology, Infectious Disease, Intrapartum Fetal Assessment, Operative Obstetrics, Obstetric Quality & Safety, Public Health-Global Health PosterSessionIV