Aspirin's safety in pregnancy questioned.

A new study fails to support the belief that aspirin can safely prevent high blood pressure during most pregnancies.

Previous research had indicated that daily aspirin use could prevent preeclampsia--dangerously high blood pressure that can occur during gestation--in pregnant women at high risk of this condition (SN: 7/13/91, p.22).

Those results led some doctors to prescribe a baby aspirin a day for pregnant patients, even those at relatively low risk of the hypertensive disorder. Despite that trend, no one had ever studied aspirin's safety and efficacy in these low-risk pregnancies.

The new research, detailed in the Oct. 21 NEW ENGLAND JOURNAL OF MEDICINE, suggests that the risks of aspirin use may outweigh any blood pressure benefits -- at least for most pregnant women.

A team of investigators at medical centers across the country randomly assigned 3,315 healthy women pregnant with their first child into two groups. Women in one group received a low dose of aspirin (approximately one baby aspirin) each day, while volunteers in the control group got dummy pills.

The researchers the monitored the pregnancies, checking each recruit's blood pressure and urine samples.

The team discovered that preeclampsia occurred 4.6 percent of the time in the aspirin group and 6.3 percent of the time in the control group. They concluded that aspirin did lower the risk of preeclampsia, but the benefit was small.

Aspirin's value appeared to be limited to one very specific group of women -- those who had entered the study with a systolic blood pressure that was slightly elevated although still within the normal range.

For most women, aspirin proved far from risk-free. The team found that women in the aspirin group faced an increased risk of abruptio placentae, a life-threatening condition for mother and fetus in which the placenta separates from the uterus.

"Based on our results in this study ... we recommend that low-dose aspirin not be used as a prophylactic in first-time pregnant women," says study coauthor Robert C. Cefalo of the University of North Carolina at Chapel Hill.