Abstract

Rationale A growing body of literature links both depressive symptoms generally, and those specifically in the postnatal period, with an inflammatory immune response. Evolutionary medical approaches, such as the Pathogen Host Defence Theory of Depression (PATHOS-D), have likened depression to sickness behaviour in other mammals, and propose that the characteristics associated with depression are protective when an individual is experiencing pathogenic threat. Many known risk factors for depressive symptoms are associated with activation of inflammatory pathways, opening up the potential for identifying novel risk factors based on their inflammation causing effects.

Objective Both the gestation of male foetuses and the experience of birth complications have documented associations with increased inflammation, yet their relationships with postnatal depression (PND) are currently unclear.

Method Here we use the complete reproductive histories of 296 women from contemporary, low fertility populations gathered by retrospective survey to assess whether the odds of PND increased when mothers gave birth to male infants or experienced birth complications, using generalised estimating equation models controlling for individual effects of the mother and other known PND risk factors.

Results We found the odds of PND increased by 71–79% when male infants were born compared to female infants. The occurrence of birth complications increased the odds of PND by 174% compared to having no complications. Testing for interaction effects found that, while always at increased risk of PND, women with a tendency towards symptoms of depression, anxiety, and stress at other points in the life course had reduced odds of PND when experiencing birth complications, suggesting such women may elicit greater support.