OBJECTIVE: The primary outcome was to determine whether magnesium sulfate therapy prolongs the duration of labor in women with mild preeclampsia. Secondary outcomes were to assess the side effects associated with magnesium sulfate therapy: hours and maximum dose of oxytocin, incidence of progression to severe preeclampsia, incidence of cesarean delivery, change in maternal hematocrit, incidence of postpartum hemorrhage, incidence of maternal infection, and Apgar scores.

STUDY DESIGN: Women with a diagnosis of mild preeclampsia at term were randomized to receive standard therapy during labor and for 12 hours post partum with either magnesium sulfate (n = 67) or a matching placebo solution (n = 68).

RESULTS: There was no difference between magnesium sulfate and placebo with respect to the primary outcome variables: total length of labor (median 17.8 hours vs 16.5 hours, p = 0.7) and length of the active phase of labor (median 5.4 hours vs 6.0 hours, p = 0.5). In addition, no difference was observed in the secondary outcome variables: hours of oxytocin use, change in hematocrit, frequency of maternal infection, progression to severe preeclampsia, incidence of cesarean delivery, and Apgar scores. Although not statistically significant, the incidence of postpartum hemorrhage was approximately fourfold greater in the magnesium sulfate group (relative risk 4.1, 95% confidence interval 0.5 to 35.4). There was a significant difference in the maximum dose of oxytocin used (13.9 ± 8.6 mU/min with magnesium sulfate vs 11.0 ± 7.6 mU/min with placebo, p = 0.036).

CONCLUSION: The use of magnesium sulfate during labor in women with mild preeclampsia at term does not affect any component of labor but did necessitate a higher dose of oxytocin. (Am J Obstet Gynecol 1997;176:623-7.)