Hypertension May Increase Risk of Birth Defects

Babies born to women who have high blood pressure during the early part of their pregnancies have an increased risk of birth defects, a new study shows, and the drugs commonly used to treat high blood pressure did not reduce this risk.

The drugs, called angiotensin converting enzyme (ACE) inhibitors, are among the most widely prescribed drugs for high blood pressure, also known as hypertension. They are known to be toxic to a developing fetus during the second and third trimesters of pregnancy, but the smaller studies that have looked at their effects during early pregnancy have produced mixed results, according to the study.

Between 1995 and 2008, researchers at the Kaiser Foundation Research Institute in California collected health information on 465,000 mother-infant pairs in the Kaiser Permanente Northern California health care system. They compared the risk of birth defects in babies born to women who took ACE inhibitors with that of babies born to women who took other drugs to treat their blood pressure, who took no drugs to treat their high blood pressure and women who didn't have high blood pressure.

The results showed that 8.5 percent of babies born to women who took an ACE inhibitor during their first trimester had birth defects, while 6.9 percent of babies born to women taking another type of high blood pressure drug had birth defects and 7.2 percent of babies born to all women in the study with high blood pressure had birth defects. Statistical tests showed that the small differences in birth defect risk between these groups could have been due to chance.

However, 5.4 percent of babies born to women without high blood pressure had birth defects — and the difference between these babies' risk and those whose mothers had hypertension was large enough to mean it wasn't due to chance.

That "suggests that it is the underlying hypertension, rather than the use of antihypertensive drugs in early pregnancy, that increases the risk of birth defects," the researchers said.

The birth defects seen in the study included congenital heart defects and defects of the brain or spinal cord.

It is reasonable to conclude that taking ACE inhibitors during the first trimester poses no greater risk of birth defects than other high blood pressure drugs, and that it is the underlying hypertension that places the fetus at risk, said Dr. Allen Mitchell, a professor of epidemiology at Boston University, who was not involved with the study.

"We have much to learn about how hypertension can cause birth defects," Mitchell wrote, in an editorial accompanying the study.

The study was published online today (Oct. 18) in the journal BMJ.

Pass it on: Blood pressure drugs may lower pregnant women's blood pressure, but they don't reduce babies' heightened risk of birth defects.

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