A woman who takes an antidepressant during the first trimester of her pregnancy does not increase her chance of delivering a baby with a birth defect, a new Canadian study shows.

The study was conducted by researchers from the Université de Montréal and the Centre Hospitalier Universitaire Sainte-Justine. They analyzed data from more than 2,300 pregnant women in Quebec. The women had been diagnosed with at least one psychiatric disorder before pregnancy and had taken antidepressants for at least 30 days in the year leading up to pregnancy.

The research team found no increased risk of delivering a baby with birth defects if a mother took antidepressants during the first 30, 60 or 90 days of her pregnancy.

The study's authors wrote that there was no significant association between antidepressant duration during the first trimester of pregnancy and the risk of major congenital malformations in infants.

Furthermore, the class of antidepressant used was not significantly associated with the occurrence of major birth defects.

The authors also found no difference in birth defect rates between women who used antidepressants during the first trimester and women who had not taken antidepressants at all during pregnancy.

The researchers also point out that studies show women with psychiatric disorders who go untreated while pregnant are at a higher risk of developing other health behaviours, such as smoking and alcohol abuse, which could negatively impact the baby.