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Twin pregnancy and severe maternal mental illness: a Canadian population-based cohort study


Twin pregnancy is a risk factor for postpartum depression and anxiety. Whether this translates into a higher risk of severe maternal mental illness in the short-term or long-term is unknown. This study was a population-based retrospective cohort study, using linked health administrative databases for the entire province of Ontario, Canada. Included were primiparas aged 15–50 years with a twin vs. singleton hospital livebirth, between January 1, 2003, and March 31, 2019. Propensity-score inverse probability of treatment weights accounted for potential confounding. The primary outcome of severe mental illness comprised a composite of an emergency department visit or hospitalization for mental illness or self-injury, or death by suicide, assessed in the first year after birth, and in long-term follow-up, up to 17 years thereafter. Fifteen thousand twenty-four twin and 796,804 (15,022 weighted) singleton births were included, with a mean (IQR) duration of follow-up of 9 (5–13) years. After weighting, the mean (SD) maternal age was 31.3 (5.5) years. In the first 365 days postpartum, severe mental illness occurred at rates of 10.5 and 8.7 per 1000 person-years in twin and singleton mothers, respectively, corresponding to a hazard ratio (HR) of 1.21 (95% CI 1.07–1.47). From 366 days onward, the corresponding figures were 5.9 and 6.1 per 1000 person-years (HR 0.96, 95% CI 0.89–1.04). Individuals with a twin birth appear to experience an increased risk for severe mental illness in the first year postpartum, but not thereafter. This suggests a potential need for targeted counselling and mental health services for mothers within the first year after birth.



Lapinsky SC, Ray JG, Brown HK, Murphy KE, Kaster TS, Vigod SN. Arch Womens Ment Health. 2023; 26(1):57-66. Epub 2023 Jan 11.

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