The research was carried out on rat cells

A team from the University of Reading has discovered that levels of a protein secreted by the placenta called neurokinin B (NKB) are raised significantly in mothers when pre-eclampsia develops.

Elevated levels of NKB can be detected as early as nine weeks of pregnancy in the mother's blood, making it potentially a very useful screening tool.

The researchers also believe that a drug that is already available - neurokinin receptor antagonist - could block the action of the protein and alleviate the condition.

However, the researchers say that clinical studies would be needed to test this theory before the drug was made widely available.

Lead researcher Professor Philip Lowry said NKB was secreted by the placenta into the mother's blood stream to stimulate an increase in blood flow to the developing foetus.

In most cases this is perfectly natural and healthy, but in women at risk of developing pre-eclampsia scientists believe the placenta fails to implant properly in the lining of the uterus.

This means that even when blood flow is increased, the foetus does not receive sufficient nutrients.

Professor Lowry believes that the placenta tries to compensate for this by pumping out even more NKB. This increases blood flow to such an extent that it causes the hypertension associated with pre-eclampsia.

Professor Lowry told BBC News Online: "We might have come up with a substance which we can measure in the blood and which should enable us to predict women who are at risk of developing pre-eclampsia.

"It could also lead on to the development of drugs that can block the life-threatening side effects of the condition."

The research, funded by the Medical Research Council, is published in the journal Nature.