An injection of "Epsom salts" could prevent thousands of cases of life-threatening eclampsia among pregnant women, say scientists.

The findings of a major international study could prompt doctors to recommend the jab for any woman showing the tell-tale early warning signs of the illness.

Pre-eclampsia is a common problem late in pregnancy, and in a small percentage of cases, it can develop into full-blown eclampsia, which endangers the life of both mother and unborn child.

The treatment could save countless lives across the world

Dr Leila Duley, Medical Research Council

The research found that if women with pre-eclampsia were given an injection of magnesium sulphate, it halved the risk of eclampsia.

The ingredient of the jab - the same as that found in Epsom salts - is cheap, and experts say it could save many lives in countries around the world.

�2.5m study

Dr Leila Duley, a Medical Research Council researcher from Oxford University, led the study.

"It is a very inexpensive treatment, making it especially suitable for use in low income countries.

"The treatment could save countless lives across the world if it was introduced routinely for pregnant women with pre-eclampsia," she said.

Another researcher, Professor James Neilson, from the University of Liverpool, said: "This is the first time that we've shown clear benefits for magnesium sulphate treatment.

"These exciting results should now change routine clinical practice across the UK and the world."

In all, hospitals in 33 countries took part in the �2.5m "Magpie" trial, which involved more than 10,000 women.

One in ten pregnant women suffers from pre-eclampsia, which is normally characterised by high blood pressure.

One in five of these have a severe form of the illness.

Fits

Severe pre-eclampsia can involve bad headaches, abdominal pain and swelling of the feet and legs.

In some cases, a baby will often have to be delivered prematurely to correct the problem.

If, from this point, the condition worsens further into eclampsia, women suffer dangerous fits.

A spokesman for the Royal College of Midwives said that new guidelines were now urgently needed.

She said: "The results of this trial are very positive and show that the proper use of magnesium sulphate is cost-effective, and above all, safe for mothers and babies."