© 2018 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY. Objective To compare the risks of adverse maternal and neonatal outcomes associated with spontaneous (SPTB) versus indicated preterm births (IPTB). Methods A secondary analysis of a multicenter trial of vitamin C and E supplementation in healthy low-risk nulliparous women. Outcomes were compared between women with SPTB (due to spontaneous membrane rupture or labor) and those with IPTB (due to medical or obstetric complications). A primary maternal composite outcome included: death, pulmonary edema, blood transfusion, adult respiratory distress syndrome (RDS), cerebrovascular accident, acute tubular necrosis, disseminated intravascular coagulopathy, or liver rupture. A neonatal composite outcome included: neonatal death, RDS, grades III or IV intraventricular hemorrhage (IVH), sepsis, necrotizing enterocolitis (NEC), or retinopathy of prematurity. Results Of 9,867 women, 10.4% (N = 1,038) were PTBs; 32.7% (n = 340) IPTBs and 67.3% (n = 698) SPTBs. Compared with SPTB, the composite maternal outcome was more frequent in IPTB-4.4% versus 0.9% (adjusted odds ratio [aOR], 4.0; 95% confidence interval [CI], 1.4-11.8), as were blood transfusion and prolonged hospital stay (3.2 and 3.7 times, respectively). The frequency of composite neonatal outcome was higher in IPTBs (aOR, 1.8; 95% CI, 1.1-3.0), as were RDS (1.7 times), small for gestational age (SGA) < 5th percentile (7.9 times), and neonatal intensive care unit (NICU) admission (1.8 times). Conclusion Adverse maternal and neonatal outcomes were significantly more likely with IPTB than with SPTB.