Psychiatric History and Postpartum Depression: The Mediating Role of Obstetric Complications

INTRODUCTION: Psychiatric history is the strongest risk factor for postpartum depression (PPD). Obstetric complications, more prevalent among women with a psychiatric history, are also independent risk factors. However, the mechanisms linking these factors to PPD remain unclear. We examined whether obstetric complications mediate the association between psychiatric history and PPD. METHODS: This cohort study utilized Danish nationwide Edinburgh Postnatal Depression Scale (EPDS) screenings (2015-2021) linked with register data. Psychiatric history was defined as psychiatric diagnoses (ICD-10: F00-99) or filled psychotropic prescriptions (ATC: N05A, N05BE01, N06A, N06BA) from 1995 until conception. Complications were defined as a composite measure of complications occurring between conception and delivery. PPD symptoms were defined as a positive EPDS score (≥ 11), and PPD diagnosis was defined as a depression diagnosis (ICD-10: F32-33) or antidepressant prescription fill (ATC: N06A indicated for depression). RESULTS: Of 170,218 mothers (163,326 in analyses), 23.9% had a psychiatric history. These mothers had higher levels of PPD symptoms (13.4% vs. 6.1%), PPD diagnosis (7.0% vs. 0.4%), and complications (34.1% vs. 28.5%) compared to those without. (A) Psychiatric history (PPD symptoms: OR = 2.32 95% CI, 2.22; 2.41; PPD diagnosis: OR = 5.09 95% CI, 4.48; 5.79) and complications (PPD symptoms: OR = 1.16 95% CI, 1.11; 1.21; PPD diagnosis: OR = 1.18 95% CI, 1.04; 1.34) were independently associated with PPD. (B) Psychiatric history did not modify the association between complications and PPD (PPD symptoms: OR = 1.20 95% CI, 1.14; 1.26 vs. 1.09 95% CI, 1.02; 1.17; PPD diagnosis: OR = 1.22 95% CI, 1.00; 1.49 vs. 1.15 95% CI, 0.97; 1.36). (C) Complications mediated only a small fraction of the association between psychiatric history and PPD (proportion mediated: PPD symptoms = 0.68% 95% CI, 0.50%; 1.00%, PPD diagnosis = 0.42% 95% CI, 0.14%; 0.79%). CONCLUSIONS: Psychiatric history and complications are independently associated with PPD, but complications explain only a negligible portion. These findings suggest that the link between psychiatric vulnerability and PPD is primarily driven by direct mechanisms rather than mediation through complications.