Postnatal depression is associated with detrimental life-long and multi-generational impacts on relationship quality.

Postnatal depression (PND) is known to be associated with a range of detrimental child and adolescent outcomes, resulting from its disruptive impact on mother-child relationship quality. However, until now little has been known about the impact of PND on the longer-term relationships between mothers and their children, and any intergenerational effects this may have. Mother-child relationship quality is of interest from an evolutionary perspective as it plays a role in the accrual of offspring embodied capital, thus affecting offspring quality and offspring's capacity to subsequently invest in their own children. Relationships with offspring also mediate grandparent-grandchild relations; if PND negatively affects long-term mother-offspring relationship quality, it is also likely to negatively affect grandmaternal investment via reduced grandmother-grandchild relationship quality. Here, we use responses to a retrospective questionnaire study of postmenopausal women, largely from the UK and US, to assess the impact of PND occurring in generation 1 on mother-child relationship quality across the life course of the child (generation 2) with whom it was associated, and also on the relationship quality with grandchildren (generation 3) from that child. Average mother-child relationship quality was lower when the child's birth was associated with PND. Multi-level regression modelling found that mother-child relationship quality decreased as PND symptom severity increased after controlling for individual effects and a variety of other factors known to influence relationship quality (individual mothers  = 296, mother-child dyads  = 646). Additionally, intergenerational relationships appear to be affected, with PND negatively associated with grandmother-grandchild relations (individual grandmothers  = 125, relations with grandchildren from  = 197 grandmother-parent dyads). That PND has long-term detrimental consequences for mother-child relationships, well beyond adolescence, highlights the need for investment in strategies to prevent PND and its cascade of negative multigenerational effects.