Magnesium sulphate was found to be highly effective in severe pre-eclampsia (relative risk 0.09, 95% confidence interval 0.01 to 0.69).² The risk of seizures without magnesium sulphate was 3.2%, and the number of women with severe pre-eclampsia who needed to be treated with magnesium sulphate to prevent one case of eclampsia was 34. Previous studies have compared the efficacy of magnesium sulphate with that of phenytoin. Based on this evidence and using a framework for making therapeutic decisions,³ obstetricians were willing to treat pre-eclamptic women with magnesium sulphate when the risk of seizures was above 2.5% and 1.75% in two UK studies (the corresponding numbers needed to treat were 57 and 77).^4,5

Coetzee et al showed that the risk of seizures without magnesium sulphate was above this risk threshold (3.2%) and that the number needed to treat (34) was below the threshold for this criterion.² There should therefore be no uncertainty about the role and choice of magnesium sulphate as a prophylactic anticonvulsant in cases of severe pre-eclampsia that warrant delivery. Moreover, further trials of magnesium sulphate versus placebo in women with severe pre-eclampsia should be unnecessary.

Idama, Tennyson O Lindow, Stephen W (Hull Maternity Hospital, Hull HU9 5LX ).

Editor—We welcome the increasing use of magnesium sulphate in the prevention of convulsions in pre-eclampsia.^1-1 We are, however, concerned that 23% of consultants would not use anticonvulsants in this clinical circumstance and that, of those who do, only 52% would choose magnesium sulphate.

Current evidence supports the use of anticonvulsants in pre-eclampsia and magnesium sulphate as the drug of choice. Coetzee et al found a significant decrease in the incidence of eclampsia in women with severe pre-eclampsia treated with magnesium sulphate compared with those treated with placebo (0.3% v 3.2%).^1-2

If we are to make substantial progress in reducing mortality from eclampsia in Britain we have to be able to prevent the first fit occurring. This conviction is supported by observations from two recent publications. In the British eclampsia survey by Douglas and Redman, 59% of 383 women with eclampsia had single fits,^1-3 and in the most recent confidential inquiry into maternal deaths, eight of the 11 women who died from eclampsia had single fits.^1-4

To our knowledge, there is no evidence that the pathophysiology of the first fit is different from that of the second and subsequent fits, and thus the concept of the first versus recurrent fits is false. We must also take account of the suggested benefits to the fetus such as protection against cerebral palsy when magnesium sulphate is given to the mother.^1-5

Use of magnesium sulphate should always be considered in pre-eclampsia until there is evidence to the contrary or the woman is entered into a study to evaluate the drug’s efficacy. Uncertainty still exists about the threshold of severity of pre-eclampsia at which magnesium sulphate should be given.