Perinatal Mental Illness and Risk of Incident Autoimmune Disease: A Population-Based Propensity-Score Matched Cohort Study

Background: Studies have demonstrated elevated risk for autoimmune disease associated with perinatal mental illness, but the extent to which this risk is specific to mental illness arising perinatally, and not mental illness generally, is unknown. Our objective was to compare the risk of autoimmune disease in women with mental illness arising within the perinatal period to (1) women with mental illness arising outside the perinatal period and (2) women who did not develop mental illness. Methods: We conducted a population-based matched cohort study of women aged 15-49 years with no history of mental illness or autoimmune disease in Ontario, Canada, 1998- 2018. The exposed, 60,701 women with mental illness arising between conception and 365 days postpartum were propensity score-matched to (1) 264,864 women with mental illness arising non-perinatally and (2) 469,164 women who did not develop mental illness. Hazard ratios (HR) for autoimmune disease were generated using Cox proportional hazards models. Results: The incidence of autoimmune disease was similar among women with mental illness arising perinatally compared to those with mental illness arising non-perinatally (138.4 vs 140.7 per 100,000 person-years; HR 0.98, 95% CI 0.92-1.05), and elevated among women with mental illness arising perinatally compared to those who did not develop mental illness (138.4 vs 88.9 per 100,000 person-years; HR 1.54, 95% CI 1.44-1.64). The HR for the latter comparison was more pronounced for autoimmune disease with brainreactive antibodies than other autoimmune disease. Conclusion: Perinatal mental illness is associated with increased risk of autoimmune disease that is no different than that of mental illness arising non-perinatally. Women with mental illness, regardless of the timing of onset, could benefit from early detection of autoimmune disease.