A test for the often fatal pregnancy complication pre-eclampsia may result from research at the University of Bristol.
It has found that low protein levels early in pregnancy indicate a risk of developing the condition, which kills 1,000 babies and up to 10 mothers a year in Britain.
The research shows that measuring levels of the protein VEGF165b at 12 weeks of pregnancy may be a good indicator of the mother-to-be's risk of getting the condition.
The tests showed that in normal pregnancies there was a 10-fold increase in VEGF165b by the 12th week while in women who went on to develop pre-eclampsia, VEGF165b had barely increased by this stage.
At full term there was statistically no significant difference between VEGF165b levels in healthy and pre-eclamptic pregnancies, suggesting that its increase is delayed in women who go on to develop pre-eclampsia.
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, said: "Developing a test to predict pre-eclampsia is a 'holy grail' in medicine.
"These researchers have made a vital finding that, if confirmed by other studies, has the potential to translate into a simple test that could potentially save many lives."