Objective: The authors previously reported strong evidence for familial aggregation of postpartum (puerperal) psychotic episodes in women with bipolar disorder. The authors here examine whether vulnerability to postpartum triggering of depressive episodes aggregates in families and assess how this aggregation varies with the definition of postpartum onset.
Method: Postpartum depression occurrence was studied in the female members of 120 sibling pairs recruited at a site within an international multicenter study of sibling pairs with recurrent unipolar depression. Employing a range of definitions of postpartum onset, the authors examined concordance for postpartum episode status between sisters.
Results: Episodes of depression with onset within 4 weeks of delivery clustered in families, but there was no significant evidence of familial clustering of broadly defined postpartum depression (onset within 6 months). Among women with a family history of narrowly defined postpartum episodes, 42% experienced depression following their first delivery, whereas only 15% of women with no such family history experienced depression following first delivery. The evidence for familiality maximized with a postpartum onset definition of 6-8 weeks.
Conclusions: These results implicate familial factors in susceptibility to the triggering of narrowly defined postpartum depressive episodes in women with recurrent major depression. They suggest that a postnatal onset definition of within 6-8 weeks of delivery may be optimal in studies of the triggering of depressive illness by childbirth.