Taking low-dose Aspirin during pregnancy may help reduce a woman's risk of a sudden increase in blood pressure, say researchers who reviewed studies on the approach.

Pre-eclampsia is a condition of pregnancy characterized by a sudden increase in blood pressure after the sixth month of pregnancy. Excess protein in the urine is another symptom.

Dr. Lisa Askie of the University of Sydney and her colleagues in Australia and the U.K. reviewed 31 studies on the effects of taking Aspirin or other antiplatelet drugs. The studies looked at more than 32,000 women and their babies.

The cause of pre-eclampsia is unclear. Complications in early pregnancy can lead to irregular blood flow to the placenta, blood clots and death of placental tissue that turn on clotting systems.

Antiplatelet drugs such as Aspirin are thought to prevent pre-eclampsia by restoring the clotting balance.

Moderate reduction

Aspirin in 75 to 150 milligram doses was linked to a 10 per cent reduction in the risk of developing pre-eclampsia, the team reports in Thursday's online issue of the medical journal The Lancet.

Women who took the drug were also 10 per cent less likely to have a premature baby delivered before 34 weeks, and to have serious pregnancy complications.

"Our data show that antiplatelet agents produce moderate but consistent reductions in pre-eclampsia and its consequences," the study's authors concluded.

Pre-eclampsia is "almost a certainty" in women with pre-eclampsia in more than one pregnancy or chronic hypertension with pre-eclampsia in a previous pregnancy, said gynecology Prof. James Roberts of the University of Pittsburgh and Dr. Janet Catov of Magee-Women's Research Institute of Obstetrics, also in Pittsburgh.

"In these settings, Aspirin is justified," the pair said in a journal commentary.

In the more usual setting when the risk is about 20 per cent, such as chronic hypertension, carrying multiples, pre-pregnancy diabetes or pre-eclampsia in one previous pregnancy, it is harder to judge if the benefits of Aspirin outweigh the theoretical long-term risks, they said.

"Is treating 50 women to prevent one case of pre-eclampsia or one preterm birth worthwhile?" the pair asked.

The number might seem worthwhile from a public health perspective but the decision is probably best left to an informed woman and her doctor, they said. Aspirin is not recommended for people with stomach problems.

Pre-eclampsia occurs in about eight per cent of pregnancies, and the risk is higher with first pregnancy, advanced maternal age and a past history of diabetes, high blood pressure, or kidney disease, according to the U.S. National Institutes of Health.