Magnesium sulphate more than halves the risk of eclampsia, and probably reduces maternal death. There is no clear effect on outcome after discharge from hospital. A quarter of women report side effects with magnesium sulphate.
Magnesium sulfate in women with mild preeclampsia: a randomized controlled trial.
To determine whether magnesium sulfate prevents disease progression in women with mild preeclampsia.
                A total of 222 women with mild preeclampsia were randomized to receive intravenous magnesium sulfate (n = 109) or matched placebo (n = 113). Mild preeclampsia was defined as blood pressure of at least 140/90 mm Hg taken on two occasions in the presence of new-onset proteinuria. Patients with chronic hypertension or severe preeclampsia were excluded. Patients were considered to have disease progression if they developed signs or symptoms of severe preeclampsia, eclampsia, or laboratory abnormalities of full or partial HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome.
                The groups were similar with respect to maternal age, ethnicity, gestational age, parity, and maternal weight at enrollment. Fourteen women (12.8%) in the magnesium group and 19 (16.8%) in the placebo group developed severe preeclampsia after randomization (relative risk = 0.8, 95% confidence interval 0.4, 1.5, P =.41). None in either group developed eclampsia or thrombocytopenia. Women assigned magnesium had similar rates of cesarean delivery (30% versus 25%), chorioamnionitis (3% versus 2.7%), endometritis (5.3% versus 4.3%), and postpartum hemorrhage (1% versus 0.9%), compared to those assigned placebo. Neonates born to women assigned magnesium had similar mean Apgar scores at 1 and 5 minutes as those born to women assigned placebo (7.7 +/- 1.5 versus 7.8 +/- 1.6 and 8.7 +/- 0.7 versus 8.8 +/- 0.6, respectively).
                Magnesium sulfate does not have a major impact on disease progression in women with mild preeclampsia. Magnesium use does not seem to increase rates of cesarean delivery, infectious morbidity, obstetric hemorrhage, or neonatal depression.