The objective of this study was to use modern analysis and reporting methods to present the full results of the first randomized trial of antenatal corticosteroids, performed 50 years ago.

In this single-center trial, women at risk of preterm birth at 24 to less than 37 weeks of gestation were randomized to receive 2 doses of betamethasone or placebo, 24 hours apart. Women and their caregivers were blinded to treatment allocation. The primary outcome was respiratory distress syndrome. Secondary outcomes included measures of neonatal mortality and morbidity, mode of birth, and maternal infection.

Between 1969 and 1974, 1115 women (1142 pregnancies) were randomized, 560 pregnancies (601 infants) to betamethasone and 582 (617 infants) to placebo. The risk of respiratory distress syndrome was significantly reduced in the betamethasone group compared with placebo (8.8% vs 14.4%, adjusted relative risk 0.62, 95% CI 0.45-0.86, P = .004). Subgroup analyses indicated greater efficacy in male than female infants but no effect of tocolytic therapy or doubling of betamethasone dose. Fetal or neonatal death, neonatal or maternal infection, neonatal hypoglycaemia, cesarean delivery, and lactation status at discharge were not different between the groups.

Antenatal betamethasone administered to women at risk of preterm birth between 24 and less than 37 weeks of gestation reduces the incidence of respiratory distress syndrome, with greater effect in male than in female infants. Doubling the dose of betamethasone does not provide additional benefit.