Taking an antidepressant like Paxil may increase a pregnant woman’s risk of having a baby with a birth defect. Although some researchers suggest that the chances appear remote and confined to a few so-called “rare” defects, those defects can be substantial.

The findings appeared in The New England Journal of Medicine. www.nejm.org GlaxoSmithKline www.gsk.com claims that antidepressants are not a major cause of serious physical problems in newborns.

Here’s the problem with these studies: they didn’t include enough cases to adequately assess risks and they didn’t include information on how long women were taking antidepressants or at what doses.

“These are important papers, but they don’t close the questions of whether there are major effects” of these drugs on developing babies. That’s what Dr. Timothy Oberlander said. He’s a developmental pediatrician at the University of British Columbia www.ubc.ca who was not involved in the studies. “There are many more chapters in this story yet to be told.”

In both studies, researchers interviewed mothers of numerous infants with birth defects, including heart valve problems. They found that mothers who remembered being on antidepressants like Paxil while pregnant were at no higher risk for “most” defects than a control group of women who said they had not taken antidepressants. But they are at higher risk for some birth defects.

For example, the study led by Carol Louik of Boston University www.bu.edu found that use of Paxil was associated with an increased risk of a heart defect in a newborn.