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138 Contemporary trends in adverse neonatal outcomes Courtney-Lynn V. Stahl, Robert M. Rossi, Emily A. DeFranco Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine, Cincinnati, OH OBJECTIVE: ACOG published guidelines in 2013 with specific delivery timing recommendations for various medical and fetal conditions in an effort to reduce maternal and neonatal morbidity. We sought to determine how the timing of the release of these guidelines influenced the rate of adverse neonatal outcomes. STUDY DESIGN: Using birth certificate records, we conducted a population based retrospective cohort study of all live births in Ohio from the years 2011-2012 (pre-guidelines, Epoch 1) and 2014-2015 (post-guidelines, Epoch 2). We compared frequency of composite adverse neonatal outcome defined as NICU admission, assisted ventilation (>6hrs), meconium, fetal intolerance of labor (FIOL), surfactant, seizure, low Apgar, or neonatal death between Epoch 1 and 2. We also analyzed individual adverse outcomes. We further stratified analyses by pregnancies complicated by the following medical conditions: chronic (CHTN) or gestational hypertension (GHTN), pregestational (PGD) or gestational diabetes (GDM), twin gestation, and fetal growth restriction (FGR). Other than twin gestation, analysis of each medical condition was limited to singleton births. RESULTS: 572,010 live births were included: 48.8% in Epoch 1 (20112012) and 51.2% in Epoch 2 (2014-2015). Rates of composite adverse outcomes were significantly higher in Epoch 2 compared to Epoch 1 both overall and when stratified by medical condition. Epoch 2 additionally had significantly higher rates of assisted ventilation but significantly lower rates of infant death. Each medical condition was associated with increased rates of composite adverse outcomes in Epoch 2. The risks are increased despite slight increases in preterm births <37 weeks (12.1 v 13.6%, p<0.001) and early preterm births <34 weeks (4.1 v 4.8%, p<0.001) in Epoch 2. However, neonatal and infant death rates decreased significantly in cases of GHTN and twin gestation. Infant death rates also decreased in pregnancies with FGR and GDM.