Infants born to mothers taking antidepressants while pregnant are more likely to have reduced head growth, according to a new study, published Monday in the Archives of General Psychiatry.

Although selective serotonin reuptake inhibitors (SSRIs) like Paxil and Prozac relieved depression in pregnant women, researchers found that the drugs appeared to be associated with greater preterm birth risk.

Researchers noted that untreated depressive symptoms in pregnant women were linked to a reduction in total body growth, including the fetal head, but prenatal SSRI use was related only to reduced fetal head growth but did not affect the growth of the fetal body.

Investigators at the Sophia Children's Hospital and Erasmus Medical Center, Rotterdam, the Netherlands, studied babies born to 7,696 pregnant women, and 570 women were depressed but were not taking medication and 99 women were depressed and taking SSRIs.

Children born to mothers using SSRIs had a more pronounced smaller head circumference growth than children whose mothers were also depressed but were not taking SSRIs.

Infant head circumference can be an indicator of brain weight and researchers said that small heads in infants that are from birth to four weeks old may predict future behavioral problems and psychiatric disorders. 

However, "we must be careful not to infer an association of SSRI use in pregnancy with future developmental problems," the researchers wrote in their study.

"Our findings further raise the question whether maternal SSRI treatment during pregnancy is better or worse for the fetus than untreated maternal depression, "they added.

Researchers also found that depressed mothers who did not take SSRIs during pregnancy on average gave birth a day later than usual, whereas mothers who were treated with SSRI antidepressants were twice as likely to give birth to preterm babies. 

Researchers are unsure why smaller head growth is linked to SSRIs.  They speculate that either treated women were more severely depressed than other depressed women who were not treated with SSRIs or that SSRIs directing affect fetal brain growth by the drug’s manipulation of levels of serotonin, known to play a significant role in prenatal brain development.

Study authors said that while avoiding SSRIs during pregnancy may not be practical because depression may continue even after birth and interfere with the mother’s ability to care and bond with the newborn, the risks of SSRIs must be clarified.

"Trying to balance the possible negative consequences of untreated maternal depression with the unknown potential negative consequences of SSRIs remains an open debate," they wrote. "Prescribing antidepressant medication to pregnant women is a major controversy in current psychiatry."

Other researchers have also found other risks linking antidepressants to infants still in the womb. In January in a study published in the British Medical Journal researchers found that pregnant women on antidepressants are more likely to give birth to children with persistent pulmonary hypertension.

Persistent pulmonary hypertension is an increase in blood pressure in the lungs and can lead to shortness of breath and difficulty breathing, and although rare, it is a severe disease with strong associations to heart failure.