BACKGROUND: Administration of antenatal corticosteroids (ANCS) is recommended for individuals expected to deliver between 24 and 34 weeks of gestation. However, more than 50% of individuals receive ANCS outside the recommended window. OBJECTIVE: To examine maternal and hospital factors associated with suboptimal receipt of ANCS among individuals who deliver between 24-34 weeks gestation. STUDY DESIGN: Secondary analysis of an observational study of births to 115,502 in the US from March 2008-February 2011. Data from 3123 individuals who gave birth between 240/7 to 340/7 weeks gestation, were included in this analysis. Eligible individuals' ANCS status was categorized as optimal or suboptimal (none, too late, or too early). Maternal and hospital-level variables were compared using optimal as the referent group. Hierarchical multinomial logistic regression models, with site as a random effect, were used to identify maternal and hospital-level characteristics associated with optimal ANCS use. RESULTS: Overall, 83.6% (2612/3123) of eligible individuals received any treatment: 1216 (38.9%) optimal and 1907 (61.1%) suboptimal. Within suboptimal group, 495 (15.9%) received ANCS too late, 901 (28.9%) too early and 511 (16.4%) did not receive any ANCS. Optimal ANCS varied depending on indication for hospital admission (p<0.001). The median gestational age of individuals who received optimal ANCS was 31.0 weeks. Adjusting for hospital factors, hospitals with electronic medical records and who receive transfers had fewer eligible individuals who did not receive ANCS. ANCS administration and timing varied substantially by hospital; optimal frequencies ranged from 9.1 to 51.3%, and none frequencies from 6.1% to 61.8%. When evaluating variation by hospital site, models with maternal and hospital factors, did not explain any of the variation in ANCS use. CONCLUSIONS: Optimal ANCS use varied by maternal and hospital factors and by hospital site, indicating opportunities for improvement.