Results of previous studies on the safety of antidepressants during pregnancy have been conflicting. The primary objective of this study was to investigate whether first-trimester exposure to antidepressants, specifically selective serotonin reuptake inhibitors (SSRIs), was associated with increased risk of congenital malformations. The secondary objective was to examine the effects of exposure to antidepressants during pregnancy on birth weight and gestational age.We included 63,395 women from the Norwegian Mother and Child Cohort Study. The women had completed 2 self-administered questionnaires at gestational weeks 17 and 30 on medication use and medical, sociodemographic, and psychological factors. Data on pregnancy outcome were retrieved from the Medical Birth Registry of Norway.Of the 63,395 women, 699 (1.1%) reported using antidepressants during pregnancy, most frequently SSRIs (0.9%). Exposure to SSRIs during the first trimester was not associated with increased risk of congenital malformations in general (adjusted odds ratio [OR], 1.22; 95% confidence interval [CI], 0.81-1.84) or cardiovascular malformations (adjusted OR, 1.51; 95% CI, 0.67-3.43). Exposure to antidepressants during pregnancy was not associated with increased risk of preterm birth (adjusted OR, 1.21; 95% CI, 0.87-1.69) or low birth weight (adjusted OR, 0.62; 95% CI, 0.33-1.16).This study does not suggest a strongly increased risk of malformations, preterm birth, or low birth weight following prenatal exposure to antidepressants. Without adjustments for level of maternal depression and various sociodemographic and lifestyle factors, antidepressant use during pregnancy would wrongly have been associated with an increased risk of preterm birth.