Women who use the antidepressant bupropion during early pregnancy may have an increased risk of having a baby with a particular type of heart defect, a new study suggests.

Researchers caution that it is not clear whether the medication, marketed as Wellbutrin, is the cause. And even if it is, they say, the absolute risk of the heart defect would be small - affecting just 2 out of every 1,000 infants born to women who used bupropion during the first trimester.

But the findings, published in the American Journal of Obstetrics & Gynecology, do add to questions about the risks of using antidepressants during early pregnancy.

Some studies have already linked other antidepressants - including some of the commonly used selective serotonin reuptake inhibitors (SSRIs) - to higher-than-average, though small, risks of certain birth defects.

A study last year, for example, found that among nearly half a million Danish children born between 1996 and 2003, the risk of heart defects was elevated among those whose mothers had used SSRIs such as fluoxetine (Prozac), sertraline (Zoloft) and citalopram (Celexa) during early pregnancy.

In this latest study, researchers found that among more than 12,700 U.S. infants born between 1997 and 2004, those whose mothers used bupropion during early pregnancy had more than double the risk of heart defects known as left outflow tract defects, compared with infants whose mothers had not used the drug.

Left outflow defects affect the flow of blood from the heart’s left chambers to the rest of the body. In this study, the most common type of this defect was coarctation of the aorta - a narrowing in the body’s main artery that, in children, typically requires surgical repair.

The findings do not mean, however, that depressed women on bupropion should stop taking it if they are planning a pregnancy, according to the researchers.

“I think it’s important that women understand that they should not just stop taking their medication,” said Dr. Jennita Reefhuis, a senior epidemiologist at the U.S. Centers for Disease Control and Prevention and one of the researchers on the study.

Instead, she told Reuters Health, women should talk with their doctors, ideally when they are planning a pregnancy rather than after they conceive.

The potential risk of birth defects from using antidepressants must be weighed against the risks of a woman stopping her current depression therapy, Reefhuis said.

For the study, Reefhuis and her colleagues used data on 6,853 infants born with a major heart defect and 5,869 infants with no birth defects. Of mothers whose babies were born with a heart defect, 0.5 percent reported using bupropion at some point in the month before becoming pregnant or the first trimester.

There were 10 cases of left outflow tract heart defects among mothers who had used bupropion. The drug was not linked to any other type of heart defect.

“This study needs to be replicated before we can say anything conclusive,” Reefhuis said, noting that the findings point to an association between bupropion and left outflow defects, but cannot by itself prove cause-and-effect.

If the association is causal, she said, the absolute risk to any one woman would be small. For every 1,000 births, there are an estimated 0.8 cases of left outflow tract heart defects; based on the current findings, that rate would be 2 per 1,000 among women who use bupropion in the first trimester.

Reefhuis also pointed out that with any pregnancy, the overall risk of having a baby with some form of birth defect is 3 percent.

She recommended that women on antidepressants who are planning a pregnancy talk with their doctors about their options. There are, however, no depression medications that have been established as “safe” for pregnant women, according to Reefhuis. More research on the potential effects of all antidepressants on the developing fetus is still needed, she said.

Guidelines released last year by the American Psychiatric Association and the American College of Obstetricians and Gynecologists state that psychotherapy may be an effective alternative to antidepressants for pregnant women with mild to moderate depression.

However, the guidelines say, women with a history of more severe depression, or other major psychiatric disorders, may need to continue with their medication.

Bupropion is also prescribed for smoking cessation, under the brand-name Zyban. In the case of smoking cessation, Reefhuis said, it may be easier for women to find an effective alternative to the drug.

SOURCE: American Journal of Obstetrics & Gynecology, online April 26, 2010.