Boston ? Two new studies suggest that taking antidepressants during the first trimester of pregnancy may slightly increase the risk of some rare birth defects.

But the studies, published in today’s New England Journal of Medicine, found that the overall risks are quite small. And scientists cautioned women against stopping treatment, saying that untreated depression can be even more of a danger to their offspring.

The studies were designed to find out whether a class of drugs, known as SSRIs (selective serotonin-reuptake inhibitors) posed a risk to developing fetuses early in pregnancy. They were prompted, in part, by a 2005 study suggesting that Paxil increased the rate of heart defects from about 1 percent to 2 percent.

The two studies showed no such increase in heart defects, based on reviews of thousands of infants exposed to antidepressants in the womb. But one study found slight increases in three other types of birth defects, affecting development of the skull, brain and intestines. The other study found that certain drugs were associated with a small rise in heart and intestinal problems.