Effect of intravenous magnesium sulfate on the biophysical profile of the healthy preterm fetus

Magnesium sulfate, a medication given to stop preterm labor, had no effect on the biophysical profiles of healthy preterm fetuses. Previous reports found adverse effects on this test of fetal well-being among full-term fetuses. Thirty-one fetuses between 24 and 35 weeks gestation had a biophysical profile just before their mothers were administered magnesium sulfate to stop labor. The fetuses were evaluated again at two and twelve hours after administration of magnesium sulfate. No differences in total score or in the score components were found. Possible explanations for the difference from other studies include lower dosages used, failure to rule out infection in other studies, adaptation over time, or normal differences in physiology between the preterm and the mature fetus. Longer studies should be carried out because duration of magnesium sulfate therapy may extend to one or two days.