Maintenance oral nifedipine for preterm labor: A randomized clinical trial

OBJECTIVE: This study was undertaken to evaluate the efficacy of maintenance oral nifedipine in patients initially treated with intravenous magnesium sulfate for preterm labor. STUDY DESIGN: Patients with a diagnosis of preterm labor between 24 and 33.9 weeks' gestation were randomly assigned to receive either maintenance tocolytic therapy with oral nifedipine (20 mg every 4-6 hours) or no treatment (control) after discontinuation of magnesium tocolysis. Pregnancy and neonatal outcomes were evaluated. A sample size of 50 patients was required to detect a 10-day difference in mean time gained (beta = .2, alpha = .05). Statistical analyses were based on intent to treat. The t, chi(2), and Fisher exact tests were performed. RESULTS: Seventy-four patients were randomly assigned to receive either oral nifedipine (n = 37) or no treatment (n = 37). There were no statistically significant differences in age, race, parity, preterm delivery risk factors, enrollment gestational age, results of cervical examination, delivery gestational age, time gained, or neonatal complications between the groups. Delivery gestational age (mean +/- SD) was 35.4 +/- 3.2 weeks for patients randomly assigned to receive nifedipine and 35.3 +/- 3.2 weeks for patients who received no treatment (P = .9). Time gained during pregnancy was 37 +/- 23.9 days in the nifedipine group and 32.8 +/- 20.4 days in the control group (P = .4). CONCLUSION: Maintenance therapy with oral nifedipine does not significantly prolong pregnancy in patients initially treated with intravenous magnesium sulfate for preterm labor.