A large study in Tennessee of the United States links use of ACE inhibitors in early pregnancy to major birth defects, according to a report to appear in Thursday's New England Journal of Medicine.
The use of this type of blood pressure drug had been thought as safe in the first trimester of pregnancy.
A few cases reported in the 1990s showed the use of ACE inhibitors during the late two trimesters of pregnancy led to major birth defects such as skull deformities, kidney failure, lung problems and even fetal death.
This prompted the U.S. Food and Drug Administration (FDA) to require the inclusion of the most severe warning in the product labelling to specify the risks. The labels also propose stopping taking the drugs during pregnancy.
However, there have been few tests to explore the effect on fetus by use of ACE inhibitors in the early stage of pregnancy.
The new study involved nearly 30,000 infants born between 1985 and 2000 in Tennessee. Researchers found that for the 209 mothers who took ACE inhibitor medication during early pregnancy, the risk of their babies developing major birth defects including holes in the heart, neurological and kidney problems was about 7 percent.
The risk of developing major birth defects for babies to those mothers who did not take or took other types of blood pressure drugs was about 2 percent, the study showed.
Dr. William Cooper of Vanderbilt University and other researchers considered taking ACE inhibitors during early pregnancy as unsafe. They also thought it was premature to declare other types of blood pressure drugs safe to be used in early pregnancy.
About 8 percent of pregnant women develop high blood pressure. Doctors say the condition should be controlled to avoid impact on the pregnant women and the fetus.
The FDA website is notifying doctors and patients about the increased risk of ACE inhibitors.
ACE inhibitors have been on the market for 25 years. The top sellers include Lotrel, Altace and Lisinopril.