When moms-to-be use antidepressants, their babies may be more likely to be born early or have a seizure soon after birth, a large U.S. study suggests.

The findings, reported in the American Journal of Obstetrics & Gynecology, add to evidence linking antidepressants to certain pregnancy risks - including preterm birth and smaller size at birth.

Experts are not sure if the medications, themselves, are to blame.

But in general, they say the safest course is to stop using antidepressants during pregnancy, if possible.

In the new study, researchers found that among nearly 229,000 infants born to Tennessee women, those whose moms used antidepressants during their second trimester tended to be born earlier.

When mothers filled two or three antidepressant prescriptions during the second trimester, their babies stayed in the womb for four to five days less, on average, than other babies.

In addition, newborns were more likely to have a seizure if their mother used a selective serotonin reuptake inhibitor (SSRI) during the third trimester.

SSRIs include commonly used antidepressants such as fluoxetine (Prozac), sertraline (Zoloft), citalopram (Celexa) and paroxetine (Paxil).

Newborn seizures are uncommon, however - so even with a relative increase in risk, the risk to any one baby is very small, said Dr. Richard C. Shelton, one of the researchers on the new study.

On top of that, such seizures seem to cause no long-term damage.

Still, stopping antidepressants during pregnancy if possible is the safest bet, according to Shelton, a professor at the University of Alabama at Birmingham. basic recommendation is that if a woman can come off antidepressants, that’s probably the best course to take,” Shelton told Reuters Health.

That said, depression itself is a pregnancy risk, he pointed out. So depending on the severity of a woman’s symptoms, staying with medication may be the better choice.

“Women always have to talk with their own doctors about it,” said Shelton, who was at Vanderbilt University School of Medicine in Nashville along with his co-authors at the time the research was conducted.

The findings are based on 228,876 Tennessee women who gave birth between 1995 and 2007. All were on Medicaid, the government health insurance program for the poor.

Overall, 23,280 women had been on an antidepressant before pregnancy. And most - 75 percent - stopped taking the drugs before their second trimester.

Women who were still on antidepressants during the second trimester tended to go into labor earlier.

For each prescription a woman filled during that trimester, her odds of going into labor early doubled. That was with several other factors taken into account - like a mother’s age or smoking during pregnancy.

Overall, almost 27 percent of women in the study group went into early labor - though they did not necessarily deliver early. The rate of preterm delivery was just under 14 percent.

Then there was the higher seizure risk. Among women who were on an SSRI during their third trimester, the risk of a newborn seizure climbed as the number of filled prescriptions went up.

Moms who filled three SSRI prescriptions in the last trimester were five times more likely to have a newborn who suffered a seizure, versus women not on the drugs.

However, Shelton said, newborn seizures are rare. In this study, they were seen in 0.2 percent of all infants, or one in 500.

And Shelton said this is the first study, to his knowledge, to point to a potential seizure risk with SSRIs. “I’d like to see this confirmed in other studies,” he said. “I don’t want to over-interpret the finding.”

In fact, the study cannot prove that antidepressants, per se, cause either seizures or earlier labor or birth.

For example, Shelton said, there may be something else about women who use antidepressants in the second trimester that leads to earlier labor. One possibility is that the severity of their depression is a factor.

Shelton suggested women on antidepressants plan their pregnancies and talk with their doctors about whether and when to stop the medication.

And if you notice depression symptoms re-emerging during pregnancy, Shelton said, talk to your doctor about that as well.

After giving birth, women with a history of depression are at higher-than-average risk of postpartum depression. So, Shelton said, new moms should try to notice any symptoms, and may want to consider going back on their medication.

Shelton has served as consultant to companies that make antidepressants. The other researchers on the study report no potential conflicts of interest.

SOURCE: American Journal of Obstetrics & Gynecology, online May 2, 2012