Research has been mixed on the ability of aspirin to block the development of preeclampsia, and there have been reports of side effects of aspirin, such as bleeding from the placenta.
But in the Feb. 10 issue of the British Medical Journal, researchers who reviewed 39 studies involving over 30,000 pregnant women say the balance of the evidence suggests that taking aspirin works.
"There is a benefit," says study author Lelia Duley, MD. "But it's much smaller than what people had hoped for."
Still, Duley, an obstetric epidemiologist at the Institute of Health Sciences in Oxford, U.K., says her study found that taking aspirin reduced the risk of preeclampsia by 15%. It also reduced the risk of death of the fetus or newborn by 14% and the risk of premature birth by 8%.
Those reductions may seem small, and most doctors wouldn't consider them large enough to advise all pregnant women to take aspirin, but Duley says for the women at highest risk of the condition, aspirin can and does save babies' lives.
Aspirin is a so-called "antiplatelet" drug. It is believed that aspirin and other antiplatelet medications can reverse unfavorable changes that occur in the blood and help prevent or delay the dangerous rise in blood pressure and other effects on the body from preeclampsia.
"Part of the problem is we don't know what causes preeclampsia," Duley says. "There has been an enormous amount of research activity to try to unravel what it is that causes this condition."
She says the analysis of thousands of women who have been studied and evidence of changes in the blood of women taking aspirin support the idea that aspirin can have benefit. The problem is figuring out who will benefit most since it's obvious from the studies that the benefit is somehow limited to a small group of women.
Fortunately, even though doctors are uncertain about exactly who to treat, aspirin is fairly safe as far as drugs go, says James M. Roberts, MD, director of the Magee-Womens Research Institute in Pittsburgh.
Roberts says those most likely to be given aspirin are women who had high blood pressure before getting pregnant and women who have a history of developing preeclampsia. Women who had it in a prior pregnancy are more likely to have it in a subsequent pregnancy than are women who did not have it.
Still, he says although aspirin is the only available drug to prevent preeclampsia at the moment, things may change in the not too-distant future.
"There is hope for early treatment, and there may well be better treatments than aspirin," Roberts says.
One promising class of drugs may be antioxidants. Based on good results in small studies, doctors are now getting ready to conduct larger trials of antioxidant therapy in the U.S., Canada, and the U.K. to determine how safe and effective it is in preventing the development of pregnancy-related high blood pressure conditions.
Even though aspirin is a drug commonly used by nonpregnant people, it should be used by pregnant women only with the consent and supervision of their doctor.