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Preterm labor is a clinical challenge for both expectant mothers and clinicians. New data from a randomized double-blind trial bring into question the merits of off-label administration of nifedipine, a smooth-muscle relaxant, for maintenance tocolysis. Participants (68) had experienced active preterm labor (between 24 and 34 weeks’ gestation) that had been arrested with nifedipine or magnesium sulfate. The primary outcome was attainment of 37 weeks’ gestation. Thirty-three patients received maintenance nifedipine (10 mg every 6 hours from enrollment until 37 weeks’ gestation), and 35 patients received placebo. If preterm labor recurred before 34 weeks, magnesium sulfate was administered, as appropriate.
Similar proportions of the two cohorts (39% of the nifedipine group and 37% of the placebo group; P=0.91) attained 37 weeks’ gestation. Outcomes were not altered by cervical length, gestational age, or number of gestations at enrollment. Birth weight and number of neonatal intensive care unit days were also similar between cohorts.
Lyell DJ et al. Maintenance nifedipine tocolysis compared with placebo: A randomized controlled trial. Obstet Gynecol 2008 Dec; 112:1221.
Comment
When evaluating negative results, one must consider the possibility of underpowered studies and risk for false-negative findings. The investigators powered their study to detect a 50% reduction in achieving 37 weeks’ gestation in these women with high-risk pregnancies. Perhaps a larger study would have uncovered a modest effect, or perhaps a higher nifedipine dose is necessary. Despite these issues, however, the authors rightly suggest that prolonged nifedipine treatment for tocolysis is ineffective and is not worth the associated risks.