Postpartum depression in fathers: prevalence and evaluation of selection bias in the HOPE cohort

Postpartum depression (PPD) affects both mothers and fathers, yet research on paternal PPD remains limited. The HOPE cohort includes PPD screenings using the Edinburgh Postnatal Depression Scale (EPDS) from parents in 67 of 98 Danish municipalities (2015-2021). It is the largest cohort to include fathers, and linkage with nationwide health registers provides information on PPD diagnoses, sociodemographic, and health-related factors. This cohort study aimed to evaluate potential selection bias of fathers in the HOPE cohort by comparing selected characteristics with the Danish paternal background population and estimating relative odds ratios (RORs) for three perinatal associations using logistic regression. In addition, the prevalence of paternal PPD in the HOPE cohort will be reported. In the HOPE cohort comprising 46 174 childbirths and 42 680 unique fathers, 3.29% had a positive EPDS screening, 2.69% had a registered PPD diagnosis, and 0.49% had both. Fathers in the cohort resembled the background population (444 339 childbirths) across most characteristics; however, fathers of non-Danish origin were markedly underrepresented. RORs showed no substantial differences, indicating minimal selection bias across the examined perinatal associations. Our findings suggest that fathers in the HOPE cohort are representative of fathers in the Danish background population, supporting the cohort's use for future research related to paternal mental health.