Postpartum mood episodes in bipolar I vs. II disorder: a retrospective observational analysis of clinical correlates

Background: The postpartum period is a recognized high-risk phase for maternal and infant health, yet predictors of bipolar disorder (BD) recurrence during this period remain unclear, particularly regarding distinctions between BD type I and II. This retrospective observational study assessed rates and clinical correlates of postpartum mood episodes in 248 women with a history of at least one pregnancy, affected by BD I (n:89) and BD II (n: 159). Participants were divided into two groups based on the presence/absence of postpartum mood episodes. Due to non-normal data distribution (Shapiro–Wilk:0.925, p < 0.001; Kolmogorov–Smirnov:0.122, p < 0.001), group comparisons were performed using Pearson’s χ² test for categorical variables and the Kruskal–Wallis test for continuous variables. Logistic regression was used to identify clinical variables associated with a history of postpartum mood episodes. Results: Eighty-two patients (29.4%) in the overall sample had a history of postpartum mood episodes, with a higher prevalence in BD I than BD II (30.3% vs. 27.0%). A later age at BD onset was significantly associated with a lower risk of postpartum recurrences in both BD I (21.4% vs. 55.7%, p:0.010) and BD II (27.3% vs. 59.1%, p < 0.001). In BD I, women with peripartum episodes had an earlier age at menarche (36.0% vs. 10.0%, p:0.003). In BD II, those with peripartum recurrences showed an earlier age at first hospitalization (40.6 ± 13.0 vs. 51.0 ± 12.3 years, p:0.010) and higher rates of medical comorbidities (74.8% vs. 54.5%, p:0.013). Logistic regression analysis confirmed the associations observed between clinical variables and postpartum mood episode risk in both BD I and BD II subgroups. Conclusion: These findings indicate that in BD I underlying inherited constitutional factors (as age at onset and age at menarche) may influence postpartum episode risk, whereas in BD II recurrence appears more related to illness severity (such as age at first hospitalization and medical comorbidities). Given the lack of established predictors for perinatal recurrences, further studies are warranted to validate and expand these findings, enhancing the understanding of mood recurrence risk during the postpartum period.