Women with a full sister who experienced postpartum psychosis face a significantly elevated risk of developing the condition themselves, according to a large Swedish registry study discussed during the 2025 Annual Meeting of the American Psychiatric Association (APAAM25).
Published in the American Journal of Psychiatry in conjunction with APA’s Maternal Mental Health Awareness Month, the population-based study analyzed the health records of 1.6 million women in Sweden. Of those, 2,514 (0.15%) were diagnosed with postpartum psychosis within three months of their first-ever childbirth.
Relative risk significantly higher among full siblings
The adjusted relative recurrence risk for postpartum psychosis among full sisters was 10.69 (95% confidence interval [CI]=6.60–16.26), meaning affected women were more than 10 times as likely to develop the condition compared with those whose sisters had no history. In contrast, cousin-based risk was elevated but not statistically significant (relative recurrence risk = 1.78, 95% CI=0.70–3.62).
Despite the strong familial association, the absolute risk for women with an affected sister remained low – estimated at 1.60%. These findings suggest that while genetic and shared environmental factors may contribute to postpartum psychosis, the condition itself remains rare.
Overlap with bipolar disorder
The study also accounted for psychiatric history. A history of bipolar disorder in a sister doubled the risk of postpartum psychosis (odds ratio = 2.08, 95% CI=1.03–4.01). When both conditions were present in the sibling, the estimated combined odds ratio for postpartum psychosis was approximately 14.28, highlighting a potential shared but partially distinct risk architecture between the two disorders.
The analysis was based on inpatient and outpatient diagnoses from the Swedish National Patient Register, using ICD-8, ICD-9, and ICD-10 codes to identify qualifying psychiatric conditions. Diagnosis was defined broadly to reflect the absence of postpartum psychosis as a standalone category in major diagnostic systems such as DSM-5.
Implications for clinical care
Discussed during a special briefing at APAAM25, the findings provide evidence for physicians to consider familial risk factors – particularly full sibling history – when assessing postpartum psychiatric risk.
While postpartum psychosis is rare, it is considered a psychiatric emergency due to the heightened risk of suicide or infanticide if left untreated. Early identification and appropriate intervention are critical.
A step toward risk stratification
The APA emphasized that both the familial risk study and a parallel investigation into postpartum depression risk contribute to a broader understanding of maternal mental health during the perinatal period. The findings are expected to support more individualized screening and care strategies in postpartum settings.
The authors reported no conflicts of interest.
Sources:
- Kępińska AP, Robakis TK, Humphreys K, et al. Familial risk of postpartum psychosis. Am J Psychiatry. 2025;182(6). doi:10.1176/appi.ajp.20230576
- American Psychiatric Association. Two New Studies in American Journal of Psychiatry Explore Risk Prediction for Postpartum Mental Health Conditions. Published May 19, 2025. psychiatry.org