A prospective comparison of terbutaline and magnesium for tocolysis

To compare the tocolytic efficacy and side effects of parenteral and oral magnesium and terbutaline.

Ninety-eight patients in labor between 23-35 weeks were prospectively entered into a controlled trial of intravenous and oral magnesium versus subcutaneous and oral terbutaline. Tocolytic effectiveness was judged by delay of delivery for 48 hours or 1 week, and to 37 weeks or more. The need to change therapy to the alternate drug was identified, as were side effects. Entrance characteristics of the population, initial pelvic examination, and concomitant infection or cervicovaginal isolates were noted. Outcomes included gestational age at delivery, birth weights, and Apgar scores. Outcome analysis was based on initial tocolytic therapy.

Significantly more patients in the magnesium group delivered at 37 weeks or more: 34 of 46 versus 27 of 52 (P < .05). No significant differences were found for delivery by 48 hours or 1 week. The interval between treatment and delivery was greater for magnesium: 7.1 +/- 3.9 versus 5.0 +/- 3.2 weeks (P < .005). Failure to achieve 37 completed weeks was more often due to obstetric complications than to preterm labor itself. Tocolytic effectiveness was reduced if secondary therapy or re-treatment was required or if the patient had cervical dilatation of 3 cm or greater. Infectious complications were common but were not associated with tocolytic effectiveness. Side effects were more noticeable with oral magnesium and subcutaneous terbutaline.

For short-term tocolysis, no significant difference was found between magnesium and terbutaline. Magnesium was associated with a higher term delivery rate. Idiopathic preterm labor accounted for only a small part of the overall prematurity in the study population.