Prevalence and incidence of moderate and severe mental illness in the second postpartum year in England (1995-2020): a national retrospective cohort study using primary care data.

Background: Perinatal mental illness affects around 20% of women in pregnancy and the first postpartum year with little evidence regarding persistence and incidence in the second year. This study aimed to describe prevalence and incidence of moderate and severe mental illness in the second postpartum year to estimate the proportion of women who could benefit from extension of England's specialist perinatal mental health services to two years. Methods: A retrospective cohort study using United Kingdom primary care Clinical Practice Research Datalink GOLD. All women registered with a General Practitioner with third trimester, delivery code or postpartum medical record 1995-2020 were included. Secondary objectives were to investigate mental illness type and associated factors. Findings: 2,132,754 pregnancies from 1,361,497 women were included. Prevalence of mental illness likely to need specialist PMH services in second postpartum year increased significantly from 3.1% (n = 2643/85,756) in 1995 to 7.4% (n = 2473/34,098) in 2018. Incident cases increased from 1.9% (n = 1630/85,756) in 1995 to 3.8% (n = 1285/34,098) in 2018 representing 56.6% (n = 69,926/123,510) of all cases in the second year. Adjusted analysis showed odds of mental illness in second year were higher: for women in most ages vs 30-34 yrs; for each additional pregnancy (OR: 1.16, 95% CI: 1.13, 1.19 two vs one); for preterm births (OR: 1.21, 95% CI: 1.15, 1.27), near term (OR: 1.21, 95% CI: 1.17, 1.25) or post-term (OR: 1.07, 95% CI: 1.04, 1.09) vs term; with history of mental illness (OR: 2.46, 95% CI: 2.41, 2.52), smoking (OR: 1.37, 95% CI: 1.35, 1.39), substance use disorder (OR: 1.54, 95% CI: 1.48, 1.60), and for each year vs 1995. Separate analysis using a subset of data showed odds of mental illness were higher for women in all quintiles vs least deprived and for women of white ethnicity vs all other ethnicities. Although severity could not be accurately measured, most recorded illnesses would require specialist perinatal mental health input. Interpretation: Extension of specialist perinatal mental health services to two years postpartum is justified. Funding: National Institute for Health and Care Research Applied Research Collaboration West Midlands (NIHR200165).