BACKGROUND: Previous studies have shown associations between maternal infections during pregnancy and increased risks of schizophrenia and autism spectrum disorder in the offspring. However, large-scale studies investigating an association between parental infections both during and outside the pregnancy period and the risk of any mental disorder in the child are lacking.

METHODS: A nationwide Danish cohort study identified 1,206,600 children born between 1996 and 2015 and followed them to a maximum of 20 years of age. Exposure included all maternal and paternal infections treated with anti-infective agents or hospital contacts before, during, or after pregnancy. The main outcome was a diagnosis of any mental disorder in the child. Hazard ratios (HRs) were calculated using Cox regression analysis.

RESULTS: Maternal infections during pregnancy treated with anti-infective agents (n = 567,016) increased the risk of mental disorders (n = 70,037) in the offspring (HR, 1.09; 95% confidence interval [CI], 1.06-1.12), which was more elevated (p < .001) than after paternal infections (n = 350,835; HR, 1.01; 95% CI, 0.98-1.03). Maternal hospital contacts for infections (n = 39,753) conferred an increased HR of 1.21 (95% CI, 1.14-1.28), which was not significantly (p = .08) different from the risk after paternal infections (n = 8559; HR, 1.07; 95% CI, 0.95-1.20). The increased risks observed during pregnancy were not different from the similarly increased risks for maternal and paternal infections before and after pregnancy. The risk of mental disorders increased in a dose-response relationship with the number of maternal infections treated with anti-infective agents, particularly during and after pregnancy (both p < .001).

CONCLUSIONS: Maternal infections were associated with an increased risk of mental disorder in the offspring; however, there were similar estimates during and outside the pregnancy period.