Women who work during pregnancy are almost five times more likely to suffer from pre-eclampsia, the potentially fatal complication caused by high blood pressure, a study has found.

Researchers from University College Cork in the Republic of Ireland interviewed 933 women in their 20s who were still working while they were 18 to24 weeks pregnant. They found working mothers-to-be had an almost five-fold greater chance of suffering pre-eclampsia late in their pregnancies than those who stayed at home.

Professor John Higgins, the report's author, said one possibility was the stress of work increased levels of certain circulating hormones, causing a nervous system reaction that triggers high blood pressure.

His findings will be of concern to the growing number of women working until late in their pregnancy. Large numbers of Western women, especially those in professions, opt to continue working during pregnancy. One study of female physicians in America showed more than half worked up to the day before they gave birth, or the day itself.

The findings, reported in the Journal of Epidemiology and Community Health, were not affected by factors known to influence blood pressure such as smoking, drinking, weight, height and age.

The researchers wrote: "A significant independent relation was found between maternal work and ambulatory blood pressure levels in mid-pregnancy. In addition, it was found that maternal work was significantly associated with the subsequent development of pre-eclampsia."

Pre-eclampsia is a complication of pregnancy caused by a defect in the placenta that joins mother and baby and supplies the baby with nutrients and oxygen from the mother's blood. It can lead to circulation problems, including high blood pressure in the mother, and growth problems in the baby.

The condition affects one in 10 pregnancies overall and one in 50 pregnancies severely. It kills between seven and 10 mothers in Britain each year.

Mike Rich, chief executive of Action on Pre-eclampsia, said: "We know that working in pregnancy can lead to growth restriction in the baby and can increase the chances of pre-eclampsia. But it only affects those women working in hard labour or high-pressure jobs.

"Those women suffering the condition in this study suffered only the mild form in the last few weeks of the pregnancy."