A large-scale study has found a link between antidepressant (AD) use during the second and/or third trimester of pregnancy and an increased risk of autism spectrum disorder (ASD) in children by 87%.

Researchers, lead by Anick Berard, PhD, of the University of Montreal, analyzed birth data in Quebec from January 1998 to December 2009. In this time there were 145,456 babies born. The study counted all ASD diagnoses from the time of birth until date of diagnoses, death, or the conclusion of the study (December 31, 2009). The average age of the children at the final follow up was 6.24.

Those exposed to ADs in utero numbered 4724 (3.2%), of these 4200 (89.9%) were exposed during the first trimester, and 2532 (53.6%) during the second and/or third trimester. In total there were 1054 (0.72%) diagnoses of ASD. Forty-six of these diagnoses (0.97%) were exposed to ADs in utero, while 1008 (0.71%) were not. 

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Saliently, researchers found that exposure to ADs in the second and/or third trimester led to greater ASD risk, with thirty-one (1.2%) of these infants diagnosed. This represents an 87% increased risk of ASD when compared with 0.71% of ASD diagnosed infants who were not exposed to ADs. The number of average ASD diagnoses is consistent with study cases published in the last 15 years, which found approximately 0.7% diagnoses with comprisable data selections.