Psychiatric Disorders Among Fathers in Sweden Before, During, and After Partner Pregnancy.

Importance: Paternal psychiatric disorders during the perinatal period can affect the health of the entire family; however, these conditions have often been underrecognized, and little is known about their incidence and timing of onset. Objective: To investigate incidence patterns of new-onset diagnosed psychiatric disorders among men in Sweden before, during, and after a partner's pregnancy. Design, Setting, and Participants: This prospective cohort study used linked national register data for all fathers of children born in Sweden between January 1, 2003, and December 31, 2021, with follow-up from 1 year before to 1 year after pregnancy. Data were analyzed from October 1, 2024, to March 31, 2025. Exposures: The time during pregnancy and 1 year after childbirth (post partum) were considered the risk periods, while 1 year before pregnancy (before conception) was used as the reference period. Main Outcomes and Measures: Annual and weekly incidence rates (IRs) of clinical diagnoses of any psychiatric disorder and 9 type-specific disorders were calculated and standardized by age and calendar year. Adjusted Poisson regression analysis was used to further estimate incidence rate ratios (IRRs) of psychiatric disorders during and after pregnancy compared with before conception. Results: This study included 1 915 722 births from 1 096 198 fathers (mean [SD] age at childbirth, 33.8 [6.2] years) in Sweden. IRs of any diagnosed psychiatric disorder were lower during pregnancy (eg, pregnancy week 1: IR, 5.50 [95% CI, 4.69-6.31] per 1000 person-years) and the early postpartum period (eg, postpartum week 1: IR, 5.19 [95% CI, 4.41-5.97] per 1000 person-years) than in the corresponding preconception weeks (eg, preconception week 1: IR, 7.00 [95% CI, 5.97-8.04] per 1000 person-years); they returned to comparable rates later post partum. This pattern was also observed for IRRs of anxiety, alcohol use, and drug use (ie, the use of nonalcohol, nontobacco psychoactive drugs) disorders. IRRs of depression (eg, postpartum weeks 45-49: IRR, 1.30 [95% CI, 1.12-1.52]) and stress-related disorders (eg, postpartum weeks 45-49: IRR, 1.36 [95% CI, 1.15-1.61]), however, showed a notable 30% increase toward the end of the first postpartum year. In contrast, IRRs of diagnosis of tobacco use disorder, attention-deficit/hyperactivity disorder, bipolar disorder, or psychosis remained relatively stable before, during, and after pregnancy. Conclusions and Relevance: In this nationwide cohort study, fathers in Sweden were less likely to be diagnosed with a psychiatric disorder during a partner's pregnancy and early post partum than before conception, but IRs returned to comparable levels thereafter. These incidence patterns may reflect transient protection and delayed detection during the transition to fatherhood and support the need for paternal mental health surveillance, particularly for increased depression and stress-related disorders in the late postpartum period.