Psychosocial risk factors for postpartum depression and their relation to timing of onset: the Hamamatsu Birth Cohort (HBC) Study.

BACKGROUND: The time frame for postpartum depression (PPD) defined in the literature differs among studies - either 4 weeks or 3 months after childbirth. To address potential difference in PPD in relation to onset of the illness, we investigated risk factors for early- and late-onset PPD using a representative birth cohort in Japan.

METHODS: We evaluated 675 women who completed the Edinburgh Postnatal Depression Scale (EPDS) for two to three times within 3 months after childbirth. Mothers with an onset of PPD (≥ 9 points on EPDS) within 4 weeks after childbirth were classified as having early-onset PPD, and those with PPD that occurred during the period of the 5th to 12th week after childbirth were classified as having late-onset PPD. We adopted multinomial logistic regression to investigate risk factors associated with each of early- and late-onset PPD, whilst simultaneously allowing for all risk factors a priori selected in the model.

RESULTS: The period prevalence of early- and late-onset PPD was 11% and 4%, respectively. Primiparity was associated only with early-onset PPD (OR=2.6, 95%CI 1.5-4.4). Younger (<25 years: OR=3.6, 95%CI 1.2-11.2) and advanced age (≥ 35 years: OR=2.5, 95%CI 1.1-5.8) of the participating women was significantly associated only with late-onset PPD. Lack of emotional support and a history of depression/anxiety appeared to increase risk both for early- and late-onset PPD.

LIMITATIONS: Moderate sample size and diagnosis of PPD without use of structured interviews may limit generalisability of the findings.

CONCLUSION: The finding that risk sets for early- and late-onset PPD differ suggests that these two types may have different aetiology.