Bipolar Disorder Incidence During Pregnancy and in the Postpartum Period: A Population-Based Study

The postpartum period is a well-described high-risk time for bipolar episodes, but the risks during pregnancy remain debated. This study examined the incidence of bipolar disorder before, during, and after pregnancy, compared to an age-matched female population.

In this population-based study we investigated first bipolar episodes in 1,217,354 childbirths in Denmark between 2002 and 2021 (ICD-10 codes: F30-F31). We calculated the monthly incidence proportion of both inpatient and outpatient visits for bipolar disorder in mothers from 1 year before pregnancy to 1 year after delivery (perinatal period), as well as in a 1:5 matched background female cohort during the same time frame.

The incidence of bipolar diagnosis in the perinatal period was lower among mothers (0.39 per 1000 childbirths) compared to the background female population (0.82 per 1000 women), with an incidence proportion ratio of 0.47. Hospital admissions for bipolar disorder were rare during pregnancy but increased sharply postpartum, peaking in the first month. The incidence of outpatient treatment decreased in late pregnancy but rose postpartum.

Pregnancy appears to be a low-risk period for bipolar disorders, but we confirmed a well-described peak in severe episodes postpartum. Across the entire perinatal period we, however, found an overall lower incidence of bipolar diagnosis compared to the background female population. Earlier studies have described a significant bipolar diagnostic delay after psychiatric episodes in the postpartum, and we encourage increased focus on timely diagnosis.