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High BP in Early Pregnancy Increases Risk of Birth Defects


Women who have high blood pressure (BP) early in their pregnancy are more likely to give birth to infants who have birth defects, and the risk is separate from their use of antihypertensive medication. That’s the finding of a new study published in the British Medical Journal.

High BP during pregnancy poses many dangers

Women who have high BP during pregnancy, whether they develop the condition before or after conception, need to take special precautions. High BP poses a number of risks, including reduced blood flow to the placenta (which slows the baby’s growth), premature separation of the placenta from the uterus, premature delivery, the possibility of future cardiovascular disease, and preeclampsia, a potentially lethal condition for both mother and baby.

A number of studies have shown that use of antihypertensive drugs, including angiotensin converting enzyme (ACE) inhibitors and other drugs, during all three trimesters of pregnancy can result in birth defects. Researchers have not been sure, however, whether the increased risk of birth defects was associated with use of the drugs or the fact that the pregnant women had high BP. They also have been unclear about the effect of ACE inhibitors on the fetus during the first trimester.

To clear up these questions, researchers under the lead of Dr. De-Kun Li of the Kaiser Foundation Research Institute in California evaluated data from 465,754 mother-infant pairs from between 1995 and 2008. They also analyzed data concerning the women’s use of medications.

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Women who used ACE inhibitors or other drugs for high blood pressure during their first trimester showed a 20% to 22% increased risk of giving birth to an infant with a birth defect when compared with women who did not have high BP or who had not used antihypertensive medications. Compared with the women with high BP who did not take drugs (controls), there was no increased risk of birth defects associated with use of any medications for high BP.

From these findings, the authors concluded that “it is likely the underlying hypertension rather than use of antihypertensive drugs in the first trimester that increases the risk of birth defects in offspring.” According to Professor Allen Mitchell from Boston University, who commented in an accompany editorial to the study, it seems reasonable to conclude that use of ACE inhibitors during the first trimester presents no greater risk of birth defects than do other antihypertensive drugs.

Mitchell also noted that "we have much to learn about how hypertension can cause birth defects.” Given that many women who become pregnant have or develop high BP, identifying ways to successfully prevent or reduce birth defects in the offspring of these women is a challenging endeavor.

Li D-K et al. British Medical Journal 2011; 343:d5931; doi:10.1136/bmj.d5931
Mitchell AA. British Medical Journal 2011; 343:d6667; doi: 10.1136/bmj.d6667

Picture credit: Wikimedia Commons