Low levels of a key protein may help doctors to identify women at risk of pre-eclampsia mid-way through pregnancy, research suggests.
Pre-eclampsia may have a genetic cause
Scientists at the Beth Israel Deaconess Medical Center hope their findings will lead to a new screening test for the potentially fatal condition.
They found pre-eclampsia is associated with low levels of a protein in the urine linked to blood vessel growth.
Details are published in the Journal of the American Medical Association.
Pre-eclampsia, which usually develops after the twentieth week of pregnancy, causes high blood pressure.
In severe cases - and without warning - it can escalate into eclampsia, which sends the mother's blood pressure soaring, puts her life at risk, and forces premature delivery.
The condition develops in approximately 5% of all pregnancies. Worldwide, it is one of the leading causes of maternal and infant mortality.
Currently, the only way to identify pre-eclampsia is to monitor a woman's blood pressure regularly, and to test for abnormal levels of protein in the urine during the third trimester of pregnancy.
However, by the time a rise in blood pressure has been detected, it may be too late to stop the condition spiralling out of control.
Previous research by the same team suggested pre-eclampsia was linked to an imbalance of proteins called angiogenic growth factor molecules which stimulate the growth of small blood vessels.
In a normal pregnancy, the developing foetus signals to the mother's body to widen the blood vessels to the placenta, which supplies oxygen and nutrients.
However, in pre-eclampsia the these blood vessels growth narrower.
The researchers believe this is due to a complex interplay between three proteins that control this process.
In their latest study, they have shown that it is possible to detect lower than normal levels of one of these proteins - placental growth factor (PlGF) - in the urine of pregnant women who are at risk of developing pre-eclampsia.
Lead researcher Dr Ananth Karumanchi said: "Diagnosing this condition earlier could help women with pre-eclampsia avoid major complications.
"A simple urine test could help predict the onset of this disease one to two months before the onset of clinical symptoms and that could make a tremendous difference in outcomes for patients, in particular those women who have limited access to specialized medical care."
Professor Gordon Smith, an expert in obstetrics at Cambridge University, described the study as "interesting and significant".
"It could potentially make screening for women with pre-eclampsia simpler.
"However, we already have a very effective means of screening for the condition, namely, assessment of blood flow through the uterine artery (using Doppler ultrasound) at 23 weeks gestation.
"Uterine artery Doppler is an extremely good test to identify women at high risk of severe pre-eclampsia.
"The problem is that having identified women as being at high risk, we have no effective interventions to stop them going on to develop the disease.
"Tests such as uterine artery Doppler and this urine test could be useful in helping to identify women who need intensive antenatal surveillance of their blood pressure, but the major challenge is to determine how one can improve the outcome in the women found to be at high risk."
Mike Rich, of the charity Action on Pre-eclampsia said: "Research such as this is always exciting since it brings us closer to a potential test for pre-eclampsia which will help us identify women who are at higher risk of developing the disorder."