Context Childbirth has an important influence on the onset and course of bipolar affective disorder, and it is well established that there may be a delay of many years before receiving a diagnosis of bipolar disorder following an initial episode of psychiatric illness.
Objective To study to what extent psychiatric disorders with postpartum onset are early manifestations of an underlying bipolar affective disorder.
Design Survival analyses were performed in a register-based cohort study linking information from the Danish Civil Registration System and the Danish Psychiatric Central Register.
Setting Denmark.
Participants A total of 120 378 women with a first-time psychiatric inpatient or outpatient contact with any type of mental disorder excluding bipolar affective disorder.
Main Outcome Measures Each woman was followed up individually from the day of discharge, with the outcome of interest being an inpatient or outpatient contact during the follow-up period with a first-time diagnosis of bipolar affective disorder.
Results A total of 3062 women were readmitted or had an outpatient contact with bipolar affective disorder diagnoses. A postpartum onset of symptoms within 0 to 14 days after delivery predicted subsequent conversion to bipolar disorder (relative risk = 4.26; 95% CI =3.11-5.85). Approximately 14% of women with first-time psychiatric contacts during the first postpartum month converted to a bipolar diagnosis within the 15-year follow-up period compared with 4% of women with a first psychiatric contact not related to childbirth. Postpartum inpatient admissions were also associated with higher conversion rates to bipolar disorder than outpatient contacts (relative risk = 2.16; 95% CI = 1.27-3.66).
Conclusions A psychiatric episode in the immediate postpartum period significantly predicted conversion to bipolar affective disorder during the follow-up period. Results indicate that the presentation of mental illness in the early postpartum period is a marker of possible underlying bipolarity.