After tocolysis to arrest preterm labor, the patient remains at risk for preterm delivery and maintenance tocolysis is common. Few data are available on the use of nifedipine for maintenance tocolysis and the 2 randomized studies comparing nifedipine to no treatment were unblinded and had conflicting results. This prospective, randomized double-blind trial investigated the effectiveness of maintenance nifedipine tocolysis following arrested preterm labor to prolong pregnancy and improve neonatal outcomes. Between 2001 and 2007, 68 patients in active preterm labor were enrolled who were 24 to 34 weeks of gestational age, and had been treated with intravenous magnesium sulfate or oral nifedipine to arrest preterm labor. Inclusion criteria included 6 or fewer contractions per hour, intact membranes, and cervical dilation less than 4 cm. Patients were excluded who had signs of placenta previa, placental abruption, a fetal anomaly incompatible with life, intrauterine infection, or a maternal medical contraindication to ongoing tocolysis. Of the 68 patients, 33 received 20 mg nifedipine orally every 4 to 6 hours and 35 a placebo. Treatment was continued until 37 weeks of gestation. At baseline, the 2 groups were similar with regard to prior preterm birth, gestational age, and other maternal demographic characteristics. There was, however, significantly greater cervical dilation and shorter cervical length in the placebo group.
The data showed that maintenance nifedipine did not prolong gestation. No difference was found among the nifedipine and placebo groups in the percentage of patients who reached 37 weeks of gestation (39% vs. 37%, respectively, P > 0.91). Among the 2 groups, there were no differences in mean delay of delivery (nifedipine vs. placebo: 33.5 ± 19.9 days vs. 32.6 ± 21.4 days, P > 0.81), in delay of delivery for more than 48 hours or 1, 2, 3, or 4 weeks, in the mean gestational age at delivery, or in episodes of recurrent preterm labor. No significant differences in neonatal outcomes were found.
These findings are consistent with the conclusion of the American College of Obstetricians and Gynecologists that prolonged oral or parenteral tocolytic treatment is not effective in reducing preterm birth or improving neonatal outcomes.