A nationwide study from Denmark finds pregnant women have little reason to be concerned about birth defects when taking omeprazole and similar heartburn drugs.

Researchers say there is little reason to suspect such drugs - called proton-pump inhibitors, or PPIs - would harm the fetus. But with an estimated two percent of pregnant women taking them, good safety data are important.

“Medications that are most commonly used in pregnancy are among the ones that require careful study,” said Dr. Allen A. Mitchell of Boston University, who wrote an editorial about the Danish findings in the New England Journal of Medicine.

“This is the largest and best study on this subject published to date, and it offers reassurance that, as a group, PPIs don’t seem to increase the overall risk of birth defects when taken anytime in pregnancy, and particularly during the first trimester, the period when most birth defects develop,” he told Reuters Health in an e-mail.

Still, the study wasn’t large enough to rule out an effect of individual drugs on different birth defects, such as cleft lip or heart problems, Mitchell said.

Tapping into national databases, the Danish investigated nearly 841,000 births from 1996 to 2008, following the babies up to age one. In some 5,000 cases, the mothers had taken PPIs between a month before birth and the end of the first trimester.

Overall, 3.4 percent of babies whose mothers had taken the drugs had a major birth defect, compared to 2.6 percent of the babies not exposed.

Despite that clear increase, it turned out unexpectedly that only those women who had taken the medications before they got pregnant, and not after, were at risk for having a baby with birth defects.

The reasons are unclear, but it’s possible that whatever condition these women were treating could be tied to the risks.

“These results provide reassurance that PPIs, and omeprazole in particular, can be used relatively safely during the first trimester,” Dr. Bjorn Pasternak and colleague write. The study was partly funded by the Danish Medical Research Council and the Lundbeck Foundation, a commercial foundation.

Omeprazole, the most common PPI, can be bought over the counter in the U.S. for less than $20 per month. There are alternatives such as antacids, said Mitchell, but they are generally less effective against heartburn.

Experts recommend that pregnant women talk to their doctor before taking PPIs.

SOURCE:  New England Journal of Medicine, November 25, 2010.