In the Motherisk study, Canadian researchers compared perinatal outcomes of three groups of infants: (1) infants exposed to paroxetine in utero during the third trimester of pregnancy, (2) infants exposed to the drug only during the first and second trimesters of pregnancy, and (3) infants who had no drug exposure.

Although paroxetine exposure had not been associated with increased teratogenic risk, case reports of neonatal withdrawal symptoms prompted the researchers to investigate whether a discontinuation syndrome similar to that seen in adults can occur in neonates.

They found that 12 infants born to the 55 pregnant women exposed to paroxetine during the third trimester had neonatal complications that necessitated prolonged hospitalizations. The prevalent clinical picture was respiratory distress (experienced by 9 infants), hypoglycemia (experienced by 2 infants), and jaundice (1 infant).

In contrast, only 3 infants born to the 27 women using paroxetine during the first or second trimester and the 27 women using non-teratogenic drugs (54 women total) had neonatal complications. Two of those infants had been exposed to paroxetine in the first two trimesters; they had respiratory distress and meconium aspiration. The third infant, which had not been exposed to the drug, had jaundice.

"It may be argued that the high rate of adverse neonatal events, especially during breastfeeding, among infants exposed to paroxetine during the third trimester may, at least in part, be associated with the maternal psychiatric disorders associated with it," said Dr. Adriana Costei, the study's co-author and presenter. "However, half of our comparison group was comprised of mothers who had similar conditions and who received the drug only during the first trimester and second."

"Infants exposed to the drug only during the first and second trimesters did not exhibit neonatal complications or higher rates of prematurity, as did those exposed in the third trimester. This highly suggests that paroxetine exposure near term may compromise fetal and neonatal health. The fact that the adverse events were brief, without other underlying pathology, further supports drug exposure as the mechanism for the adverse effects," Costei added.

"This study is the first to highlight higher rates of perinatal complications with this drug. This means that babies exposed to paroxetine near term will need special, high-risk follow-up, to prevent long term risks," said Dr. Gideon Koren, the study's principal investigator.