Abstract
Objective: To evaluate associations between sibling psychiatric diagnoses and risk of postpartum psychosis and to determine whether these associations vary by sibling sex and the woman’s own psychiatric history.
Methods: In this population-based cohort study using Swedish national registers, we identified 1,213,829 women with a full sibling who delivered their first live-born child between January 1980 and October 2017. The primary outcome was postpartum psychosis, defined as mania, psychosis, or psychotic depression within 90 days postpartum. Associations between sibling psychiatric diagnoses and postpartum psychosis were estimated using logistic regression with cluster-robust standard errors, including stratification by the woman’s own psychiatric history.
Results: Overall, 1,831 women developed postpartum psychosis (1.5 per 1,000). The strongest associations were observed for sister’s postpartum psychosis (OR=10.84; 95% CI, 5.76–20.40), cyclothymia (OR=8.29; 95% CI, 4.65–14.76), schizoaffective disorder (OR=7.90; 4.99–12.52), and bipolar disorder (OR=5.00; 95% CI, 4.23–5.90). Patterns were similar in brother and sister pairs. Sibling psychiatric history was most informative among women with no prior psychiatric diagnosis, where sibling schizoaffective disorder (OR=4.82; 95% CI, 2.99–7.74) and bipolar disorder (OR=3.07; 95% CI, 2.59–3.64) showed substantial risk increases. Among women with a history of mania or psychosis, sibling diagnoses contributed little additional predictive value.
Conclusion: Postpartum psychosis shows strong familial aggregation across multiple sibling diagnoses, with a pattern supporting its conceptualization within the spectrum of severe mood disorders with psychotic features. Family psychiatric history may help identify at-risk women who lack established clinical predictors.
J Clin Psychiatry 2026;87(4):26m16393
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