Eclampsia is a Greek word meaning ‘bolt from the blue’. It describes one or more convulsions occurring during or immediately after pregnancy as a complication of pre-eclampsia. Eclampsia has been recognised since ancient times, but it wasn’t until the mid-nineteenth century that doctors began to realise that the fits were normally preceded by a collection of circulatory disturbances now known as pre-eclampsia. Confusingly, however, very few cases of pre-eclampsia culminate in eclampsia, while eclampsia can sometimes precede pre-eclampsia. Eclampsia is rare, affecting about 400 women per year in the UK.

When does it occur?

Eclampsia can occur at any stage during the second half of pregnancy – and some rare cases have been reported before 20 weeks. At the other extreme, the fits can occur as late as during labour or after delivery; one case has been reported as late as three weeks after delivery, although this is highly unusual. According to a recent national survey (1), 44 per cent of sufferers experience their first fit after delivery – normally within 48 hours; 38% have it in the ante-natal period and 18 per cent during labour.

Signs and symptoms

Before they suffer an eclamptic convulsion, most women have signs of pre-eclampsia, most notably high blood pressure and/or protein in the urine. Often there are one or more warning symptoms – such as restlessness, shakiness, intense headache, upper abdominal pain or visual disturbances – before the fit occurs, although these are very common, non-specific symptoms which are usually perfectly benign. For some sufferers, however, eclampsia is entirely unheralded, and signs of pre-eclampsia appear afterwards.

What is the cause?

Several factors are probably involved, including: reduced blood flow to the brain, caused by a combination of small clots and spasm of the small arteries; swelling in the brain (cerebral oedema), possibly as a complication of excessive fluid retention; bleeding from small arteries ruptured by the intensity of the blood pressure.

How is it treated?

Until recently it was assumed that conventional anticonvulsants, particularly diazepam and phenytoin, were the best agents for controlling eclampsia and preventing further convulsions. But a landmark multinational trial has now demonstrated that magnesium sulphate – the drug of choice in the US for many years – is better than either at preventing further convulsions, and may also save more lives (2). The drug is thought to work by improving blood flow to the brain, which suggests that impaired cerebral blood flow is the main cause of eclampsia. When these results were published in the summer of 1995, only 2-3 per cent of UK obstetricians were known to use magnesium sulphate, but this is likely to change in future. The drug is given by injection and is relatively straightforward to use.

However, there is no suggestion that magnesium sulphate has any effect on the underlying pre-eclamptic disorder, and a woman who recovers from eclampsia may still be at risk from other complications of the condition. There is evidence to suggest that magnesium sulphate may prevent eclamptic convulsions in women with pre-eclampsia (3), but as yet it is not possible to identify those who would benefit most from treatment.

Can it be prevented?

In theory eclampsia can be prevented by vigilant antenatal care, including a well-timed delivery. But in practice fits which occur without warning may be impossible to prevent. In the US, magnesium is routinely given to women with pre-eclampsia in the expectation that it prevents progression to eclampsia. However, this regime is not currently standard practice in the UK.

Who is at risk?

Eclampsia most commonly affects women in their first pregnancies, with teenagers and women with multiple pregnancies at highest risk. However, about one quarter of cases occur in second or later pregnancies – in most cases to women with no previous history of either pre-eclampsia or eclampsia.

What happens in the next pregnancy?

Because eclampsia is so rare its recurrence rate is not known. About one sufferer in 20 will get pre-eclampsia in the next pregnancy, with the individual risk higher for those who suffered eclampsia relatively early in the pregnancy and lower for those who had a fit at or near term. Other than this, there is no way of predicting who is most likely to suffer a recurrence and no specific means of prevention, although treatment with low-dose aspirin may be recommended in cases where the problem arose before 32 weeks (4).

For optimum safety, any woman who has suffered eclampsia in one pregnancy should be considered ‘at-risk’ in the next pregnancy. Former sufferers may like to consider preconception counselling with an expert to devise an appropriate antenatal care programme for the next pregnancy (5).


  1. The BEST (British Eclampsia Survey Team) survey analysed all cases of eclampsia occurring in the UK in 1992.  British Medical Journal 1994; 309: 1395-1400.
  2. The Collaborative Eclampsia Trial compared effectiveness of magnesium sulphate against diazepam and phenytoin in more than 1600 women with eclampsia.  Lancet 1995; 345: 1455-63.
  3. A US trial of 2,000 pregnant women with hypertension showed that those treated with magnesium sulphate were less likely to develop fits than those given phenytoin. N Engl J Med 1995; 333:201-5.
  4. Fact Sheet 1: Low-dose Aspirin for High-risk Pregnancy
  5. Consult An Expert Via APEC:  list of consultants who are considered expert in the management of all aspects of pre-eclampsia and are willing to accept referrals from GPs.