Risk, treatment duration, and recurrence risk of postpartum affective disorder in women with no prior psychiatric history: A population-based cohort study

BACKGROUND Some 5%-15% of all women experience postpartum depression (PPD), which for many is their first psychiatric disorder. The purpose of this study was to estimate the incidence of postpartum affective disorder (AD), duration of treatment, and rate of subsequent postpartum AD and other affective episodes in a nationwide cohort of women with no prior psychiatric history. METHODS AND FINDINGS Linking information from several Danish national registers, we constructed a cohort of 457,317 primiparous mothers with first birth (and subsequent births) from 1 January 1996 to 31 December 2013 (a total of 789,068 births) and no prior psychiatric hospital contacts and/or use of antidepressants. These women were followed from 1 January 1996 to 31 December 2014. Postpartum AD was defined as use of antidepressants and/or hospital contact for PPD within 6 months after childbirth. The main outcome measures were risk of postpartum AD, duration of treatment, and recurrence risk. We observed 4,550 (0.6%) postpartum episodes of AD. The analyses of treatment duration showed that 1 year after the initiation of treatment for their first episode, 27.9% of women were still in treatment; after 4 years, 5.4%. The recurrence risk of postpartum AD for women with a PPD hospital contact after first birth was 55.4 per 100 person-years; for women with postpartum antidepressant medication after first birth, it was 35.0 per 100 person-years. The rate of postpartum AD after second birth for women with no history of postpartum AD was 1.2 per 100 person-years. After adjusting for year of birth and mother's age, women with PPD hospital contact after first birth had a 46.4 times higher rate (95% CI 31.5-68.4) and women with postpartum antidepressant medication after their first birth had a 26.9 times higher rate (95% CI 21.9-33.2) of a recurrent postpartum episode after their second birth compared to women with no postpartum AD history. Limitations include the use of registry data to identify cases and limited confounder control. CONCLUSIONS In this study, an episode of postpartum AD was observed for 0.6% of childbirths among women with no prior psychiatric history. The observed episodes were characterized by a relatively short treatment duration, yet the women had a notably high rate of later AD and recurrent episodes of postpartum AD. The recurrence risk of postpartum AD was markedly higher among women with PPD hospital contact after first birth compared to women with postpartum antidepressant medication after first birth. Our results underline the necessity of measures targeted at specific vulnerable groups, such as women who experience PPD as a first psychiatric episode.