Magnesium sulphate and other anticonvulsants for women with pre-eclampsia

Magnesium sulphate helps prevent eclamptic fits in pregnant women with pre-eclampsia ('toxaemia').

Some women have high blood pressure with protein in their urine during pregnancy (pre-eclampsia, or 'toxaemia'). Most women with pre-eclampsia give birth without problems. However, severe pre-eclampsia can cause problems such as stroke, kidney failure, liver failure, and blood clotting. A few women have seizures (eclampsia). These problems can lead to the baby being born too small or too soon. If the woman has eclampsia, both she and her baby are at high risk of death. Eclampsia is most common in low- and middle-income countries.

This review of 15 studies showed magnesium sulphate reduced the number of women having eclampsia, but did not improve the babies' health. Magnesium sulphate had side effects for the mother, mostly flushing. Follow-up of women and children is reassuring that there are no adverse effects later on.

Authors' conclusions: 

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.

Read the full abstract...

Eclampsia, the occurrence of a seizure (fit) in association with pre-eclampsia, is rare but potentially life-threatening. Magnesium sulphate is the drug of choice for treating eclampsia. This review assesses its use for preventing eclampsia.


To assess the effects of magnesium sulphate, and other anticonvulsants, for prevention of eclampsia.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (4 June 2010), and the Cochrane Central Register of Controlled Trials Register (The Cochrane Library 2010, Issue 3).

Selection criteria: 

Randomised trials comparing anticonvulsants with placebo or no anticonvulsant, or comparisons of different drugs, for pre-eclampsia.

Data collection and analysis: 

Two authors assessed trial quality and extracted data independently.

Main results: 

We included 15 trials. Six (11,444 women) compared magnesium sulphate with placebo or no anticonvulsant: magnesium sulphate more than a halved the risk of eclampsia (risk ratio (RR) 0.41, 95% confidence interval (CI) 0.29 to 0.58; number needed to treat for an additional beneficial outcome (NNTB) 100, 95% CI 50 to 100), with a non-significant reduction in maternal death (RR 0.54, 95% CI 0.26 to 1.10) but no clear difference in serious maternal morbidity (RR 1.08, 95% CI 0.89 to 1.32). It reduced the risk of placental abruption (RR 0.64, 95% CI 0.50 to 0.83; NNTB 100, 95% CI 50 to 1000), and increased caesarean section (RR 1.05, 95% CI 1.01 to 1.10). There was no clear difference in stillbirth or neonatal death (RR 1.04, 95% CI 0.93 to 1.15). Side effects, primarily flushing, were more common with magnesium sulphate (24% versus 5%; RR 5.26, 95% CI 4.59 to 6.03; number need to treat for an additional harmful outcome (NNTH) 6, 95% CI 5 to 6).

Follow-up was reported by one trial comparing magnesium sulphate with placebo: for 3375 women there was no clear difference in death (RR 1.79, 95% CI 0.71 to 4.53) or morbidity potentially related to pre-eclampsia (RR 0.84, 95% CI 0.55 to 1.26) (median follow-up 26 months); for 3283 children exposed in utero there was no clear difference in death (RR 1.02, 95% CI 0.57 to 1.84) or neurosensory disability (RR 0.77, 95% CI 0.38 to 1.58) at age 18 months.

Magnesium sulphate reduced eclampsia compared to phenytoin (three trials, 2291 women; RR 0.08, 95% CI 0.01 to 0.60) and nimodipine (one trial, 1650 women; RR 0.33, 95% CI 0.14 to 0.77).