Comparison of magnesium sulfate, terbutaline and a placebo for inhibition of preterm labor. A randomized study

Magnesium sulfate has been recommended as a safe and effective agent for inhibiting preterm labor. Its reported adequacy as a tocolytic agent, however, has not been substantiated by randomized, controlled trials. To assess the efficacy of magnesium sulfate, we initiated a prospective, randomized study comparing the capabilities of magnesium sulfate, terbutaline and a placebo (5% dextrose in lactated Ringer's solution) for labor inhibition. The study population consisted of 54 patients between 26 and 34 weeks of gestation and in preterm labor. The diagnosis of labor was made if, following hydration, persistent uterine contractions occurred at a frequency of at least three in a ten-minute period and cervical examination suggested active labor. Success was defined as postponement of delivery for at least 48 hours after initiation of therapy. Despite a trend toward increased efficacy in the terbutaline group there were no significant differences between the three treatment groups with regard to capability of delaying delivery at least 48 hours. Also, there were no significant differences between the groups with regard to gestational age at delivery, birth weight and neonatal survival. The fact that delivery occurred in less than 48 hours of approximately one-half the patients under the best of circumstances emphasizes the need for more effective techniques for the inhibition of preterm labor and the need for a better understanding of the mechanisms involved in the initiation of preterm labor.