Magnesium sulfate compared with nifedipine for acute tocolysis of preterm labor: a randomized controlled trial

To compare the efficacy and side effects of intravenous magnesium to oral nifedipine for acute tocolysis of preterm labor.

A multicenter randomized trial was performed. Patients in active preterm labor who were at 24 to 33 weeks and 6 days of gestation were randomly assigned to receive magnesium sulfate or nifedipine. The primary outcome was arrest of preterm labor, defined as prevention of delivery for 48 hours with uterine quiescence.

One hundred ninety-two patients were enrolled. More patients assigned to magnesium sulfate achieved the primary outcome (87% compared with 72%, P=.01). There were no differences in delivery within 48 hours (7.6% magnesium sulfate compared with 8.0% nifedipine, P=.92), gestational age at delivery (35.8 compared with 36.0 weeks, P=.61), birth before 37 and 32 weeks (57% compared with 57%, P=.97, and 11% compared with 8%, P=.39), and episodes of recurrent preterm labor. Mild and severe maternal adverse effects were significantly more frequent with magnesium sulfate. Birth weight, birth weight less than 2,500 g, and neonatal morbidities were similar between groups, but newborns in the magnesium sulfate group spent longer in the neonatal intensive care unit (8.8+/-17.7 compared with 4.2+/-8.2 days, P=.007).

Patients who received magnesium sulfate achieved the primary outcome more frequently. However, delay of delivery, gestational age at delivery, and neonatal outcomes were similar between groups. Nifedipine was associated with fewer maternal adverse effects.