However, this latest study contradicts previous research that found that taking antidepressants in pregnancy can be risky.
The question is an important one because depression is common in pregnancy. It's diagnosed in 10 percent to 20 percent of pregnant women, and up to 13 percent of women take antidepressants while pregnant, according to the researchers.
"The most critical period in the development of an embryo or in the growth of a particular organ is during the time of most rapid cell division," said Krista Huybrechts, lead study author and epidemiologist at the Brigham and Women's Hospital, in Boston. So, it is in the first three months of pregnancy that the risk for developing major malformations is highest, she explained.
The U.S. government-funded research was published in the June 19 issue of the New England Journal of Medicine.
The current study's findings run counter to two previous studies that caused the U.S. Food and Drug Administration in 2005 to formally warn health care professionals that early prenatal exposure to paroxetine (Paxil) may increase the risk of heart malformations at birth.
Huybrechts and her team had some concerns about the earlier research and wanted to re-examine the evidence by designing their study differently. They tightened the focus and took more factors that could interfere with the data into account, she said. The team looked at whether antidepressants, including those called selective serotonin reuptake inhibitors, or SSRIs -- such as paroxetine (Paxil) and sertraline (Zoloft) -- are indeed associated with an increased risk of heart defects at birth.
The researchers tapped data from 46 states and Washington, D.C., from 2000 through 2007. They were able to use demographic information, such as age, income and education, as well as data about all physician services and hospitalizations, including diagnoses, procedures and filled outpatient prescriptions.
A total of almost a million women who had given birth were included in the study. They were all on Medicaid without supplementary private insurance. All of the women were between 12 to 55 years of age. Women were excluded if they had been treated with drugs that have been associated with birth defects (such as chemotherapy, lithium, retinoids and thalidomide) or if their infants had been diagnosed with a genetic abnormality.
A total of about 64,000 (6.8 percent) of the women used antidepressants in the first three months of pregnancy. After adjusting the data to account for other factors that might increase the risk of a heart defect, the researchers found almost no difference in the risk of a baby being born with a heart defect between mothers who had been on antidepressants and those who hadn't.
But one expert does not find the results of the study reassuring. "While this is an excellent group of researchers, there are some serious flaws with this study," said Dr. Adam Urato, maternal-fetal medicine specialist at Tufts Medical Center, in Boston.
"This isn't rocket science. We know that exposing developing babies to synthetic chemicals is almost always a really bad idea and should be avoided whenever possible," said Urato. "This study does nothing to alter that common sense conclusion."
Urato said there were several specific problems with the study. Analysis of the huge database was likely to have misclassified whether women were indeed taking their antidepressants (not just picking up the prescription), which would make the medications look safer than they actually are, he explained.
The study didn't identify miscarriages, which are linked to antidepressants. "It may be that the most severely affected pregnancies are miscarrying," Urato said.
And he questioned why evidence of smoking and weight issues weren't considered in the data analysis. "We know that smoking is common in a Medicaid population and that it's associated with heart defects," Urato said, "and body mass index [a measurement based on height and weight] may also influence this."
Urato added that because current research suggests that antidepressant use -- especially SSRIs like Paxil and Zoloft -- is associated with increased risk of miscarriage, birth defects, preterm birth, early rupture of membranes, preeclampsia (high blood pressure associated with pregnancy), and neurological problems in newborns, among other issues, pregnant women should not take them.
As for a potential risk of suicide in a woman who is pregnant and seriously depressed, Urato said the evidence still suggests antidepressants are an unsafe option. "The evidence is that antidepressant use is associated with suicide in young people who take those medications," he said.
So, where does that leave a depressed woman who is pregnant?
"The best available current evidence strongly suggests that for most women, nondrug approaches to mental health issues such as psychotherapy and exercise provides as much -- or more -- benefit than chemical antidepressants," said Urato. These nondrug therapies should be tried first in women who are pregnant or of childbearing age, he added.
Learn more about pregnancy and depression from the U.S. Centers for Disease Control and Prevention.