Perinatal mental illness in Ontario (2007-2021): A population-based repeated cross-sectional surveillance study.

Objective: Perinatal mental illness can negatively impact pregnant and postpartum women and gender-diverse birthing persons, their children, and families. This study aimed to describe population-level trends in perinatal mental health service use, including outpatient and acute care contacts, to guide decisions about investments in evidence-based treatment.

Methods: In this repeated cross-sectional population-based surveillance study in Ontario, Canada, we measured monthly rates of mental health service use for perinatal people (conception to 1 year postpartum) from January 2007 to December 2021. Event rates were calculated by dividing the number of contacts in a given month by the total eligible perinatal time for that month expressed in per 1000 person-months. Rates by service type (outpatient, acute care), diagnosis, and sociodemographic characteristics, and by history of pre-existing mental illness were also calculated.

Results: In total, 22-28% of perinatal people had perinatal mental health service use annually (10-15% in pregnancy, 17-21% in postpartum). Perinatal mental health outpatient care rates decreased initially (2007-2012), stabilized, and then increased after March 2020. Acute care rates were stable from 2007 to 2015, then increased (especially for anxiety and substance/alcohol use disorders). Across all contact types, the highest rates were in postpartum vs. pregnancy, those aged < 25 and > 40 years, non-immigrants, urban-dwellers, and those with pre-existing mental illness.

Conclusion: Ensuring rapid access to evidence-based supports and services for perinatal mental illness is essential. Groups with increased need based on sociodemographic and clinical characteristics may benefit from targeted supports and services to ensure optimal treatment and prevent adverse outcomes.