Pregnancy risk from blood pressure drugs?

Babies exposed in the first trimester of their mother's pregnancy to blood pressure drugs called ACE inhibitors are at an increased risk of birth defects, according to a new study. The drugs already carry a warning against their use dining the second and third trimesters of pregnancy because of the danger of kidney damage in the fetus.

A review of the records of 29,507 infants in Tennessee showed that 209 babies had been exposed to ACE inhibitors during the first trimester in the womb. The records reveal that the mothers of another 202 babies had taken other blood pressure drugs during the first trimester and the rest of the infants had no exposure to blood pressure medicines.

The records showed that 7.1 percent of the children exposed to ACE inhibitors had congenital defects--mainly of the heart and central nervous system--compared with only 1.7 percent of the babies exposed to other blood pressure drugs and 2.6 percent of those not exposed, researchers report in the June 8 New England Journal of Medicine.

ACE inhibitors target angiotensin converting enzyme (ACE). Normally, ACE converts the compound angiotensin I into angiotensin II, which induces the blood vessels to constrict and blood pressure to rise. By suppressing ACE, the inhibitors relax blood vessels and lower blood pressure.

Why ACE inhibitors might damage a fetus is unclear, says study coauthor William O. Cooper, a pediatrician at Vanderbilt University School of Medicine in Nashville. "Most organ formation occurs in the first trimester" he says. "It's not likely that relaxing blood vessels led to these problems. It looks like angiotensin plays a role in organ formation."