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473 Trial of labor after cesarean in preterm deliveries: is success different from TOLAC at term? Rebecca R. Rimsza, William M. Perez, Gross A. Gilad, Laura K. Vricella Saint Louis University, Division of Maternal Fetal Medicine, Saint Louis, MO OBJECTIVE: There is limited data on trial of labor after cesarean (TOLAC) outcomes in preterm deliveries and commonly available vaginal birth after cesarean (VBAC) success calculators do not include gestational age. We sought to evaluate TOLAC success in preterm and term deliveries. STUDY DESIGN: This was a retrospective cohort study of patients undergoing TOLAC at an academic tertiary institution (2011-2017). Previable deliveries, fetal demise, and multiple gestations were excluded. Preterm (24e 36 weeks) and term (37+weeks) deliveries were compared. Primary outcome was VBAC success. Secondary outcomes were composite neonatal morbidity (umbilical pH< 7.0, 5minute APGAR < 7, unanticipated NICU admission) and composite maternal morbidity (ICU admission, hysterectomy, uterine rupture). VBAC success was then evaluated by gestational week and a stepwise linear regression was performed for predictors of VBAC success. Univariate analysis was performed. P < 0.05 was significant. RESULTS: A total of 1379 patients undergoing TOLAC met study criteria and were analyzed. Gestational age at delivery ranged from 24 0/7 to 42 3/7 weeks. 1193 (87%) were term and 186 (13%) were preterm. Maternal age and previous vaginal delivery were greater in preterm TOLACs (p .001 for both), but prior cesarean for arrest was similar in term and preterm (p 1⁄4 .3). Preterm deliveries had greater VBAC success than term (75 vs. 83%, p < .007). Composite maternal and neonatal morbidities were similar (p .2, table). Preterm VBAC success was higher than term in both spontaneous (89 vs 80%) and induced labor (64% vs 61%) (p 1⁄4 .001 for both). VBAC success decreased with advancing gestation (Figure, p 1⁄4 .001). After controlling for confounders, increasing gestational age remained predictive of decreasing VBAC success [F (3,37) 1⁄4 6.4, p < .001], R1⁄4 .272. CONCLUSION: Preterm deliveries had greater VBAC success than term deliveries in spontaneous and induced labor. TOLAC should be considered as an option for both term and preterm deliveries.