The effect of magnesium sulfate on fetal heart rate variability and uterine activity.

The effect of magnesium sulfate on fetal heart rate (FHR) variability and uterine activity is evaluated in 19 preeclamptic patients at term in active labor. Magnesium sulfate was given by intramuscular injection in nine patients and by intravenous infusion in 10 patients after an intravenous loading dose over a period of 15 minutes. No significant change was noted in FHR variability. There was only a transient, mild decrease in the frequency of uterine contractions during the magnesium sulfate loading dose, and there was no significant change in the intensity of uterine contractions. The conclusion is that, when magnesium sulfate is used for treatment of mild preeclampsia in patients at term in established labor, there is no clinically significant effect on FHR variability or uterine activity.