Genetic influences on post-natal depressive symptoms: findings from an Australian twin sample

Background. Conflicting evidence exists on causes of vulnerability to post- natal depression. We investigated genetic and environmental influences on v ariation in post-natal depressive symptoms (PNDS) following first live birt h, and sources of covariation with the personality trait Neuroticism and li fetime major depression occurring post-natally (DEP-PN) and at other times (DEP-XPN) to test for shared genetic influences. Method. Retrospective interview and questionnaire data from 838 parous fema le twin pairs (539 monozygotic, 299 dizygotic) from the Australian National Health and Medical Research Council volunteer adult twin register were use d for multivariate genetic model-fitting. Data on PNDS were evaluated for c onsistency with diagnostic interview assessment. Results. Genetic factors explained 38 % of variance in PNDS (95 % confidenc e interval 26-49 %) and 25 % of the variance in interview-assessed DEP-PN. The genetic correlation between PNDS and lifetime major depression (DEP-PN and DEP-XPN) was low (r(g) = 0.17, 95 % confidence interval = 0.09-0.28), s uggesting that the questionnaire was measuring a construct other than postn atally occurring major depression, possibly post-natal dysphoria. Associati ons between PNDS and obstetric factors were very modest. Conclusions. Findings suggest modest genetic influences on major depression occurring postnatally. Independent and stronger genetic influences identif ied for post-natal symptomatology or dysphoria (PNDS) justify further inves tigation.