A study designed to compare magnesium sulfate and nifedipine as treatments for preterm labor involved 192 women who were in active preterm labor at 24 to nearly 34 weeks gestation. Of those, 92 women were randomly chosen to receive I.V. magnesium sulfate and 100 women received sublingual and oral nifedipine. Treatment continued until at least 12 hours of uterine quiescence was achieved in 48 hours. (Uterine quiescence was defined as six or fewer contractions per hour.)

Comparing responses with the two drugs, researchers found no differences in delivery within 48 hours, gestational age at delivery, birth before 37 and 32 weeks, and episodes of recurrent preterm labor. But women who'd received magnesium sulfate were significantly more likely to experience mild and severe adverse reactions, such as lethargy, nausea and vomiting, dizziness, shortness of breath, pulmonary edema, hypotension, and chest pain.

Birth weights and neonatal complications were similar between the two groups, but infants whose mothers had received magnesium sulfate stayed in the neonatal ICU more than twice as long (8.8 days versus 4.2 days).

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