Is High Blood Pressure Linked to Birth Defects?

Oct. 18, 2011 -- A new study may put hypertension during pregnancy under more scrutiny.

Women who take blood pressure drugs called ACE inhibitors during the first trimester of their pregnancy may be no more likely to have babies with birth defects than women with hypertension who take other types of high blood pressure medication or no blood pressure drugs at all, according to a new study.

These findings run counter to a 2006 study that showed women who took ACE inhibitors -- but not other blood-pressure-lowering drugs -- during the first trimester were at greater risk for having babies with heart malformations and other types of birth defects.

The new study suggests that it may be the underlying high blood pressure that increases the risk of birth defects, regardless of treatment. Women who had high blood pressure during pregnancy were at greater risk for all types of birth defects, particularly heart malformations and neural tube defects.

The findings appear in the journal BMJ.

ACE inhibitors taken during the second and third trimester of pregnancy have been previously linked to birth defects. These drugs must carry a “black box” warning from the FDA concerning these risks. A black box warning is the FDA's most serious warning.

Researchers analyzed data on 465,754 pairs of moms and babies from 1995 to 2008, including information on which medications they were taking. Overall, women who took any blood pressure medication as well as those with untreated high blood pressure were more likely to have a baby with some type of birth defect.

The new study did not look at how high blood pressure during early pregnancy results in birth defects, but Li suggests that it may reduce blood flow to the developing fetus.

Reassuring News for Some Women

The findings are somewhat reassuring for women who became pregnant while they are taking ACE inhibitors, says Howard Strassner, MD. He is the chairman of the department of obstetrics and gynecology at Rush University Medical Center in Chicago.

About half of all pregnancies are unplanned, so many women may be taking high blood pressure medications when they learn they are pregnant. ACE inhibitors are commonly prescribed to lower blood pressure.

Women who have any underlying medical conditions, including high blood pressure, should ideally discuss these issues with their doctor before they become pregnant, says Eva K. Pressman, MD. She is professor of obstetrics and gynecology and director of maternal and fetal medicine at the University of Rochester.

ACE Inhibitors Risky in Late Pregnancy

"In the ideal world, they would change medications first, but if they are on an ACE inhibitor and become pregnant, they can switch to another by second trimester," she says.

Treating high blood pressure during pregnancy is important, she says. Women who have high blood pressure during pregnancy are at risk for complications including preterm birth and preeclampsia, a potentially fatal pregnancy-related condition, she says.

"The data would suggest that there may be a modest increase in the risk of certain birth defects among women with hypertension, whether it is treated or not," says Allen A. Mitchell, MD, in an email. Mitchell, the director of the Slone Epidemiology Center at Boston University Schools of Public Health & Medicine in Boston, wrote an editorial accompanying the new study.

"Apart from adopting lifestyle behaviors that might reduce the likelihood of developing hypertension (such as diet and exercise), women who do have hypertension may actually take some reassurance from this and earlier reports because they suggest that the medications used to control hypertension do not seem themselves to pose a substantial risk to the fetus,” he says.

"At the same time, it is important for the health of both mother and infant to control maternal hypertension, since the complications of this condition can be quite serious to both."