In a subsequent report, Hall and associates 76 enrolled 318 women with preeclampsia – mostly severe and remote from term and not in labor – who were managed expectantly with antihypertensive drugs and without magnesium sulfate. Interestingly, two of the three postpartum seizures occurred beyond 48 hours and thus would not have been eligible for their standard magnesium sulfate regimen. Five patients (0.5%) developed eclampsia: two (0.4%) in the magnesium group – both before delivery – and three (0.6%) in the no magnesium group – all postpartum. Odendaal and Hall 75 reported 1001 such women, of whom 510 received magnesium sulfate prophylaxis based upon the clinical impression of impending eclampsia, while 491 women did not. Studies that support this conclusion include two large prospective observational studies from the same medical center in South Africa that describe the rate of eclampsia in women with severe preeclampsia who did not receive prophylactic magnesium sulfate. There is now general agreement that magnesium sulfate should be given to prevent convulsion in women with severe preeclampsia. Magnesium Sulfate for Severe Preeclampsia Based on a rate of eclampsia of 0.5%, and assuming 50% reduction by magnesium sulfate, to a 0.25% rate, with an α of 0.05 and a β of 0.2, at least 9383 women would need to be enrolled in each group to document a significant reduction in eclampsia. In order to determine the effectiveness or safety of magnesium sulfate with certainty, there is a need for a multicenter placebo-controlled trial of magnesium sulfate prophylaxis for mild preeclampsia. Importantly, the trial indicates that magnesium sulfate is superior to phenytoin for seizure prophylaxis in such women. These findings suggest that the rate of seizures in women with mild hypertension or mild preeclampsia receiving phenytoin is 0.6% or treated women. Four of the 10 women with seizures had severe preeclampsia. As shown in Table 12.8, there were no seizures among 1049 women assigned to magnesium sulfate, but there were 10 cases of eclampsia – 1% – among 1089 women assigned to phenytoin ( p=0.004). 72 over 2000 women with gestational hypertension – only a small percentage had severe preeclampsia – were randomized to either intramuscular magnesium sulfate or an intravenous/oral phenytoin regimen. 69–72 Only one of these was sufficiently powered to evaluate seizure prophylaxis in these women and the other three evaluated mostly side effects of magnesium therapy. There have been four randomized trials that compared magnesium sulfate with phenytoin for women with various pregnancy hypertensive disorders ( Table 12.8).
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