Around 600 babies and five women die each year in Britain as a result of the condition, which is caused by a defect in the placenta that leads to high blood pressure and kidney problems for the woman.
In the early stages, there are no symptoms and it is only as the condition develops that headaches, shoulder pain, nausea and swelling of hands and feet occur.
In the UCL study, published in the journal Hypertension, researchers tested the urine of 27 women who developed preeclampsia and 47 who did not.
They found the protein inositol phosphoglygan P-type was several times higher in women who developed the condition – and its presence in urine could be found up to seven weeks before a clinical diagnosis would normally be possible.
They believe the protein may in fact be the toxin that causes the condition. If confirmed in further studies, this could lead to the development of treatments to reverse the effects of the protein and so protect women and babies from serious complications.
Around one woman in ten suffers pre-eclampsia during pregnancy. One in 50 will suffer severe symptoms.
The only way to cure it is to deliver the child. But if this is done too soon, the child may be too premature to survive.
Professor Thomas W Rademacher from UCL said: ‘Being able to predict the onset of this disease has been the single greatest challenge in obstetric medicine.
‘Pre-eclampsia is the most common of the serious complications that can occur during pregnancy.’
Professor Rademacher said the presence of the protein appears to be ‘a reliable indicator’ of whether a woman will develop the condition.
He added: ‘This means that by way of a simple urine test during pregnancy, we can identify which women are most at risk of developing the condition.
This is a test I would like to see offered to expecting moms. I am in favour for any non-invasive test that could give the doctor more knowledge about what is going on with your body.