Heritability of postpartum depression in female twin pairs: A Danish population-based cohort study

Postpartum depression (PPD) is a common but severe psychiatric condition following childbirth, and its underlying causes and degree of heritability remain unclear. We aimed to examine the heritability of PPD among parous female twin pairs.

We linked data from the Danish Twin Register to nationwide health registers. Zygosity was defined as monozygotic (MZ) or dizygotic (DZ) based on validated questionnaires, and PPD was defined using hospital diagnosis of depressive disorders or filled prescriptions of antidepressant medication during the first year postpartum. We used a classic twin design to estimate genetic variance in PPD liability, applying probandwise concordance rates, tetrachoric correlations, and biometric modeling to decompose phenotypic variance into genetic and environmental components.

The study included 10,418 female twins (5209 pairs) born from January 1949 to December 2000. There were 68 PPD-discordant and 10 PPD-concordant MZ pairs and 85 PPD-discordant and 5 PPD-concordant DZ pairs. The probandwise concordance rates were 0.22 (95% confidence interval (CI) 0.13-0.35) for MZ twins and 0.11 (95% CI 0.05-0.23) for DZ twins. The heritability (additive genetic effect) of PPD was 0.60 (95% CI 0.46-0.75) with a corresponding unique environment variance of 0.40 (95% CI 0.25-0.54).

The results indicate that heritability explains a substantial part of PPD risk. This knowledge is pivotal to understanding the role of genetics and to reducing the stigma of PPD among new mothers. However, the contribution of environmental and other possible modifiable factors emphasizes the importance of targeted prevention initiatives.