Background Infants born at 34 to 36 weeks’ gestation (late preterm) have greater risks of adverse respiratory and other outcomes, than those born at 37 weeks gestation or later. It is not known whether betamethasone administered to women at risk for late preterm delivery decreases risks of neonatal morbidities. Methods We conducted a multicenter randomized trial of women with a singleton gestation at high risk for late preterm delivery. Participants were randomized to two injections of 12 mg betamethasone or matching placebo 24 hours apart. The primary outcome was a neonatal composite of treatment in the first 72 hours (continuous positive airway pressure or high flow nasal cannula for at least two hours, supplemental oxygen with a fraction of inspired oxygen of at least 30 percent for at least four hours, extra corporeal membrane oxygenation or mechanical ventilation) or stillbirth or neonatal death before 72 hours. Results 2,831 patients were randomized. The primary outcome occurred in 11.6% of the betamethasone group versus 14.4%, in the placebo group (Relative Risk 0.80, 95% confidence interval 0.66-0.97, P=0.02). Severe respiratory morbidity, transient tachypnea of the newborn, surfactant use, and bronchopulmonary dysplasia were also significantly less common in the betamethasone group. There were no significant differences between groups in the incidence of chorioamnionitis or neonatal sepsis. Neonatal hypoglycemia was more common in the betamethasone group. (24.0% versus 14.9%, RR 1.61, 95% CI 1.38-1.88, P<0.001) Conclusions Administration of betamethasone to women at risk for late preterm delivery significantly reduced the rate of neonatal respiratory morbidity.

Background-Infants born at 34 to 36 weeks' gestation (late preterm) have greater risks of adverse respiratory and other outcomes, than those born at 37 weeks gestation or later. It is not known whether betamethasone administered to women at risk for late preterm delivery decreases risks of neonatal morbidities.