Mothers who have postnatal depression are unlikely to have more than two children according to research carried out by evolutionary anthropologists the University of Kent and published by Evolution, Medicine and Public Health.
Until now very little has been known about how women's future fertility is impacted by the experience of postnatal depression.
A research team from Kent's School of Anthropology and Conservation collected data on the complete reproductive histories of over 300 women to measure the effect postnatal depression had on their decision to have more children. The mothers were all born in the early to mid-20th century and the majority were based in industrialised countries while raising their children.
The team concluded that postnatal depression, particularly when the first child is born, leads to lowered fertility levels. Experiencing higher levels of emotional distress in her first postnatal period decreased a woman's likelihood of having a third child, though did not affect whether she had a second.
Furthermore, postnatal depression after both the first and the second child dissuaded women from having a third child to the same extent as if they had experienced major birth complications.
The research by Sarah Myers, Dr Oskar Burger and Dr Sarah Johns is the first research to highlight the potential role postnatal depression has on population ageing, where the median age of a country becomes older over time.
This demographic change is mostly caused by women having fewer children, and can have significant social and economic consequences. Given that postnatal depression has a prevalence rate of around 13% in industrialised countries, with emotional distress occurring in up to 63% of mothers with infants, this research suggests that investing in screening and preventative measures to ensure good maternal mental health now may reduce costs and problems associated with an aging population at a later stage.
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Postnatal depression and reproductive success in modern, low-fertility contexts; Sarah Myers, Oskar Burger, Sarah E. Johns; Evolution, Medicine, and Public Health  pp. 71–84; DOI: 10.1093/emph/eow003