Objectives To evaluate the efficacy of weekly administration of antenatal corticosteroids compared with a single course in reducing the incidence of neonatal morbidity and to evaluate potential complications of weekly treatment.

Design and Setting Randomized, double-blind, placebo-controlled intention-to-treat trial conducted in 13 academic centers in the United States from February 1996 through April 2000.

Participants A total of 502 pregnant women between 24 and 32 completed weeks' gestation who were at high risk of preterm delivery.

Intervention All patients received a complete single course of antenatal corticosteroids (either betamethasone, 12 mg intramuscularly repeated once in 24 hours for 2 doses, or dexamethasone, 6 mg intramuscularly repeated every 12 hours for 4 doses). Participants who had not delivered 1 week after receipt of the single course were randomly assigned to receive either betamethasone, 12 mg intramuscularly repeated once in 24 hours for 2 doses every week until 34 weeks' gestation or delivery, whichever came first (n=256), or a similarly administered placebo (n=246).

Main Outcome Measure Composite neonatal morbidity (including severe respiratory distress syndrome, bronchopulmonary dysplasia, severe intraventricular hemorrhage, periventricular leukomalacia, proven sepsis, necrotizing enterocolitis, or perinatal death).

Results Composite morbidity occurred in 22.5% of the weekly-course group vs 28.0% of the single-course group (unadjusted relative risk, 0.80; 95% confidence interval, 0.59-1.10). Neither group assignment nor the number of treatment courses was associated with a reduction in composite morbidity.

Conclusions Weekly courses of antenatal corticosteroids did not reduce composite neonatal morbidity compared with a single course of treatment. Weekly courses of antenatal corticosteroids should not be routinely prescribed for women at risk of preterm delivery.