Newborns face little risk of birth defects from the antidepressants taken by many women early in pregnancy, say the reassuring findings of the two biggest studies of this controversial link.

The research focuses on the class of drugs chosen most often for depression and anxiety, including the brands Prozac, Paxil and Zoloft.

Paxil carries a warning of possible heart defects in newborns, and experts don't expect the new research to change that. However, they find the new studies comforting for women struggling with depression.

The possibility of birth defects from antidepressants has put doctors and patients in a quandary.

Birth defects obviously hurt newborns, but depressed mothers who can't give proper care also endanger their babies.

Confusing matters, researchers have wondered if the concern about birth defects should extend beyond Paxil to this entire class of drugs, known as selective serotonin-reuptake inhibitors, or SSRIs.

The two latest studies, appearing Thursday in The New England Journal of Medicine, relieve some of that worry, say birth specialists.

Risk 'pretty small'

"Yeah, there's a risk, but the risk overall is probably pretty small," said Dr. Susan Ramin, obstetrics chair at the University of Texas Medical School in Houston, who was familiar with the findings.

The two studies — one from the federal Centers for Disease Control and the other from Boston University — use more cases of birth defects than previous research to consider links between the abnormalities and SSRIs. The Boston University study was funded partly by the National Institutes of Health and Paxil maker GlaxoSmithKline PLC.

Together, the two studies looked at 19,471 newborns with birth defects and 9,952 without them. Then they considered what SSRIs the mothers in both groups took during the first three months of pregnancy and mapped the patterns of birth defects.

Neither study was able to tie SSRIs as a group to either heart defects or most other defects.

That reassurance is especially welcome because depressed women fret even more than other mothers about the health of their newborns, said Dr. Stephan Quentzel, a psychiatrist who treats pregnant women at Beth Israel Medical Center in New York City.

Also, a mother's untreated depression can lead to poor care or turmoil at home, a weaker maternal bond, and other problems for a newborn.

"The fetus and the newborn are almost always worse off if the mom is depressed than if … exposed to the vast majority of antidepressants," Quentzel said.

Weigh risks, benefits of drugs before pregnancy

However, doctors and mothers have been very wary about medications and birth defects since Europe's thalidomide scandal of deformed babies in the early 1960s. Defects from all causes are expected in about three per cent of births, enough to make many mothers nervous.

The concern about SSRIs grew out of GlaxoSmithKline's own alert in 2005 about possible heart defects in newborns whose mothers took Paxil early in pregnancy. The U.S. Food and Drug Administration and Health Canada added their own warnings. Last year, a separate study linked SSRIs taken late in pregnancy to a lung disorder  in newborns.

The latest studies do not consider that disorder, known as persistent pulmonary hypertension. But they suggest that the risk of other defects from an SSRI, even if confirmed, would add only a fraction of one per cent to the overall danger, researchers said.

Paxil did appear to triple the risk of a defect in blood flow from the heart, both studies found. But that additional danger would still be modest, experts said.

The studies further hinted at possible ties between other SSRIs and a handful of other defects, but researchers said the numbers of newborns with specific defects were too small to draw strong conclusions.

Researchers said women should talk over the potential risks and benefits with their doctors, preferably before pregnancy.