Doctors at Wake Forest University Baptist Medical Center in North Carolina found that angiotensin levels increased by around 50% during normal pregnancies.

Understanding the mechanism and whether these levels serve as a marker are the first steps in developing preventive therapy

Dr David Merrill

When pre-eclampsia occurred the boost in angiotensin did not kick in, so blood pressure was not kept in check.

Dr David Merrill, specialist in obstetrics and foetal and maternal medicine at the centre, said that, while the cause of pre-eclampsia is still a mystery, the research indicated a possible trigger for the condition.

"Additional research is needed to show if low levels of angiotensin early in a pregnancy can predict pre-eclampsia and if levels can be altered to prevent the disorder," he said.

Urine measurement

Researchers from Wake Forest also measured the level of angiotensin in urine samples, finding a steady increase in the first three months of pregnancy and a peak in the seventh month.

The peak levels were 13 times higher than in women who were not pregnant.

"Pre-eclampsia is one the major problems in obstetrics," said Dr Merrill.

"Understanding the mechanism and whether these levels serve as a marker are the first steps in developing preventive therapy."

Jacqui Jablaoui, director of the UK support group, Action on Pre-eclampsia welcomed the research, but said much more needs to be done.

"It is very exciting that there is the possibility of some kind of predictor but we really need a much bigger trial to confirm this," she told BBC News Online.

She pointed out that other trials, such as using magnesium sulphate to treat the condition and vitamins A and E to prevent it, also had a long way to go.

"But it is good news that people are people are carrying out research into what is the most common complication of pregnancy," she added.