Chronic physical conditions and risk for perinatal mental illness: a population-based retrospective cohort study

Background — One in five women experience mental illness in pregnancy or postpartum. Universal preventive interventions have not lowered the incidence of perinatal mental illness, perhaps because those at highest risk were not targeted. Outside of pregnancy, chronic physical conditions are known to confer increased risk for mental illness. Our objective was to examine the association between chronic physical conditions and risk of perinatal mental illness.

Methods and Findings — We conducted a population-based retrospective cohort study using linked health administrative datasets in Ontario, Canada, in 2005-2015. We compared 77,385 women with chronic physical conditions to 780,619 women without such conditions, all of whom had a singleton livebirth. Excluded were women with a mental illness diagnosis within 2 years before pregnancy. Chronic physical conditions were captured using the Agency for Healthcare Research and Quality Chronic Condition Indicator, applied to acute healthcare encounters in the 2 years before pregnancy. The outcome was perinatal mental illness, defined by a mental illness or addiction diagnosis arising between conception and 365 days postpartum. The outcome was further defined by timing (prenatal or postpartum) and specific diagnosis (psychotic disorder, mood or anxiety disorder, substance use disorder, self-harm, or other). Modified Poisson regression generated relative risks (aRR) and 95% confidence intervals (CI), adjusted for age, parity, rural residence, income quintile, and remote history of mental healthcare. Women in the cohort had an average age of 29.6 years (standard deviation 5.4), 44.2% 36 were primiparous, 11.0% lived in a rural area, 40.1% were in the lowest two income quintiles, and 47.9% had a remote history of mental healthcare. More women with (20.4%) than without (15.6%) a chronic physical condition experienced perinatal mental illness—an aRR of 1.20 (95% CI 1.18-1.22, p<.0001). The aRRs were statistically significant for mental illness in pregnancy (1.12, 95% CI 1.10-1.15, p<.0001) and postpartum (1.25, 95% CI 1.23-1.28, p<.0001). Psychotic disorders (aRR 1.50, 95% CI 1.36-1.65, p<.0001), mood or anxiety disorders (aRR 1.19, 95% CI 42 1.17-1.21, p<.0001), substance use disorders (aRR 1.47, 95% CI 1.34-1.62, p<.0001), and other mental illness (aRR 1.68, 95% CI 1.50-1.87, p<.0001) were more likely in women with than without chronic physical conditions, but not self-harm (aRR 1.14, 95% CI 0.87-1.48, p=.34). The study was limited by reliance on acute healthcare encounters to measure chronic physical conditions and the inability to capture undiagnosed mental health problems.

Conclusions — Findings from this study suggest that women with a chronic physical condition predating pregnancy may be at heightened risk of developing mental illness in the perinatal  period. These women may require targeted efforts to lower the severity of their condition and improve their coping strategies and supports in pregnancy and thereafter.