AARON B. CAUGHEY, PER SANDBERG, MARYA ZLATNIK, JULIAN T. PARER, MARIPAULE THIET, RUSSELL K. LAROS JR, University of California, San Francisco, Obstetrics, Gynecology and Reproductive Sciences, San Francisco, California, California Pacific Medical Center, Obstetrics and Gynecology, San Francisco, California OBJECTIVE: To compare perinatal outcomes between forceps and vacuum assisted deliveries. Our hypothesis was that the force vectors achieved in forceps delivery will lead to fewer shoulder dystocia, but greater perineal lacerations. STUDY DESIGN: This is a retrospective cohort study of 4120 term, cephalic, singleton, operative vaginal deliveries at a single institution. Outcomes examined included rates of shoulder dystocia, perineal and cervical lacerations, and neonatal trauma. Potential confounders including maternal age, birthweight, ethnicity, parity, gestational age, station at delivery, episiotomy, attending physician, anesthesia, and lengths of 1st and 2nd stages of labor were controlled for using multivariate logistic regression. RESULTS: In the study population, there were 2045 (49.6%) forceps and 2075 (50.4%) vacuum assisted deliveries. Of note, the rate of shoulder dystocia was higher among women undergoing vacuum assisted delivery (3.5% vs. 1.5%, P! .001). Other differences are reported in the table below. These differences in perinatal complication rate persisted when controlling for the confounders listed above with adjusted odds ratio for shoulder dystocia being 3.05 (95% CI 1.85– 5.04), and 3rd or 4th degree lacerations being 0.65 (95% CI 0.55–0.75) when comparing vacuum to forceps. CONCLUSION: Vacuum assisted vaginal birth is more often associated with shoulder dystocia and cephalohematoma. Forceps delivery is more often associated with 3rd and 4th degree perineal lacerations as well as cervical lacerations. These differences in complications rates should be considered among other factors when determining the optimal mode of delivery.