BACKGROUND: Gestational age at birth is a potentially important modifiable risk factor in neonates with congenital heart disease. We evaluated the relationship between gestational age and outcomes in a multicenter cohort of neonates undergoing cardiac surgery, focusing on those born at early term (ie, 37-38 weeks' gestation). METHODS AND RESULTS: Neonates in the Society of Thoracic Surgeons Congenital Heart Surgery Database who underwent cardiac surgery between 2010 and 2011 were included. Multivariable logistic regression was used to evaluate the association of gestational age at birth with in-hospital mortality, postoperative length of stay, and complications, adjusting for other important patient characteristics. Of 4784 included neonates (92 hospitals), 48% were born before 39 weeks' gestation, including 31% at 37 to 38 weeks. Compared with a 39.5-week gestational age reference level, birth at 37 weeks' gestational age was associated with higher in-hospital mortality, with an adjusted odds ratio (95% confidence interval) of 1.34 (1.05-1.71; P=0.02). Complication rates were higher and postoperative length of stay was significantly prolonged for those born at 37 and 38 weeks' gestation (adjusted P<0.01 for all). Late-preterm births (34-36 weeks' gestation) also had greater mortality and postoperative length of stay (adjusted P=0.003 for all). CONCLUSIONS: Birth during the early term period of 37 to 38 weeks' gestation is associated with worse outcomes after neonatal cardiac surgery. These data challenge the commonly held perception that delivery at any time during term gestation is equally safe and appropriate and question the related practice of elective delivery of fetuses with complex congenital heart disease at early term.