A Cochrane review (abstract , review ) included 15 studies with a total of 15 892 subjects; 6 studies with a total of 11 444 women compared magnesium sulphate with placebo or no anticonvulsant. There was more than a halving in the risk of eclampsia associated with magnesium sulphate (RR 0.41, 95% CI 0.29 to 0.58; NNT 100, 95% CI 50 to 100). The risk of dying was non-significantly reduced by 46% for women allocated magnesium sulphate (RR 0.54, 95% CI 0.26 to 1.10). For serious maternal morbidity RR was 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; NNT 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; NNTH 6, 95% CI 5 to 6).
Follow-up was reported by one trial comparing magnesium sulphate with placebo: there was no clear difference in death (RR 1.79, 95% CI 0.71 to 4.53; 3 375 women) or morbidity potentially related to pre-eclampsia (RR 0.84, 95% CI 0.55 to 1.26) (median follow-up 26 months). In children (n=3 283) 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 (RR 0.08, 95% CI 0.01 to 0.60; 3 studies, n=2 291) and nimodipine (RR 0.33, 95% CI 0.14 to 0.77; 1 study, n=1 650).