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Birth Defects Likely Linked to Hypertension, Not Early Use of ACE Inhibitors in First Trimester of Pregnancy, According to New Research

OAKLAND, Calif. — Women who take ACE inhibitors, a type of drug commonly used to treat high blood pressure, in the first trimester of their pregnancy are at no greater risk of having babies with birth defects than are women who have taken other types of high blood pressure medications, a new study from the U.S. Department of Health and Human Services’ (HHS) Agency for Healthcare Research and Quality (AHRQ) found. The study, conducted at the Northern California Kaiser Permanente Division of Research, suggests that the underlying high blood pressure itself may increase the risk of birth defects, rather than blood pressure medications taken during the first trimester of pregnancy.

ACE (angiotensin-converting enzyme) inhibitors are among the most widely prescribed drugs used to treat hypertension, particularly among people who also have diabetes. ACE inhibitors are known to raise the rate of birth defects in the second and third trimesters of pregnancy, and one earlier study reported a link between the use of ACE inhibitors and birth defects in the first trimester of pregnancy.

The new AHRQ report is based on an observational, retrospective study led by De-Kun Li, MD, PhD, a perinatal epidemiologist at the Northern California Kaiser Permanente Division of research. The study, which looked at the large and ethnically diverse Northern California Kaiser Permanente population, did not find a unique link between first-trimester ACE inhibitor use and birth defects.

Results of the study, prepared for AHRQ’s Effective Health Care Program by the HMO Research Network—a member of AHRQ’s Developing Evidence to Improve Decisions about Effectiveness (DEcIDE) Network—were published today in BMJ.

“Some women of child-bearing age have high blood pressure, and about half of them will get pregnant while taking one or more medications to treat it,” said AHRQ Director Carolyn M. Clancy, M.D. “This report should lead to informed discussions by women, in consultation with their doctors, about the best way to manage their high blood pressure, particularly if they become pregnant.”

ACE inhibitors are oral medications that are prescribed to treat high blood pressure. They are also used commonly to treat heart failure and to protect some people from diabetes complications. Yet because they work by inhibiting an enzyme in the kidney, physicians counsel caution in taking them in the second and third trimesters of pregnancy, a crucial period of development for the unborn baby. ACE inhibitors carry a “black box” warning from the Food and Drug Administration—that agency’s strongest warning—against their use in the second and third trimesters of pregnancy.

A study published in 2006 that examined nearly 30,000 births over 15 years to mothers enrolled in Tennessee’s Medicaid system suggested that pregnant women who took ACE inhibitors in the first trimester of pregnancy had babies with birth defects at approximately 3 times the rate of mothers who were not taking any medicines for high blood pressure. But the new AHRQ study—which examined more than 465,000 babies born over 13 years in the Kaiser Permanente Northern California region—found no such correlation. The new report found that birth defects occurred at the same rate among all women with high blood pressure, regardless of whether they took ACE inhibitors, other antihypertensive drugs, or no antihypertensive drugs at all.

While the AHRQ study could not conclude that high blood pressure is explicitly to blame for increased birth defects, researchers said that the findings suggest that underlying hypertension likely results in increased birth defects. Thus, taking steps to reduce blood pressure before pregnancy—including losing weight and reducing sodium intake—may reduce the risk of birth defects.

The study, Maternal Exposure to Angiotensin Converting Enzyme Inhibitors in the First Trimester and Risk of Malformations in Offspring: A Retrospective Cohort Study, is the latest study from AHRQ’s Effective Health Care Program. The Effective Health Care Program helps patients, doctors, nurses, pharmacists and others choose the most effective treatments by sponsoring the development of evidence reports and technology assessments to assist public- and private-sector organizations in their efforts to improve the quality of health care in the United States. More information about the program can be found at

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