Each year, an estimated three million pregnant women throughout the world develop a potentially serious condition, and around 75,000 of them die.

The condition, called pre-eclampsia, can be caught by monitoring the mother's blood pressure, but the method is not perfect. Researchers are working to development a blood test that could be more accurate.

Pre-eclampsia can develop suddenly, usually in the second half of a woman's pregnancy. The condition can lead to a more serious disease called eclampsia that can cause convulsions in pregnant women and result in death of both the mother and child. Researchers at Harvard University and Beth Deaconess Hospital in Boston have identified a marker or substance in the blood that appears to increase the risk of pre-emclampsia in women.

In a study involving 280 women, half with pre-eclampsia and half without, the substance, called s-FIT1, was three-times higher in the blood of those who had had pre-eclampsia than women without the condition.

Carin Solomon, deputy editor of the New England Journal of Medicine, where the research was published, says there's a need for such a blood test.

"By the time blood pressure is up, the process is clearly already in the works," she said. "And the interesting finding here is that particularly this marker, called s-FIT1, was rising steeply and clearly elevated before these clinically signs were apparent."

But Dr. Solomon notes s-FIT1 levels could be elevated by genetic factors, diabetes and a deficiency of calcium in the diet, among other things.

Study author Vikas Sukhatame, a kidney expert at Beth Deaconess Hospital in Boston, agrees. "So there are bunch of other groups that still need to be looked at and looked at carefully," he said.

A blood test for pre-eclampsia may not be that far off. A study found the condition could be accurately detected in rats with elevated s-FIT1.