There is compelling evidence that children of mothers with postnatal depression (PD) experience poor developmental outcomes. However, no studies have specifically ascertained the risk of mortality for offspring during preschool years, the most catastrophic outcome in the vulnerable period. This nationwide population-based study aimed to investigate whether maternal depression in the first year after giving birth was associated with increased mortality risk among their preschool children aged up to 5 years.

Three nationwide population-based datasets [the National Health Insurance Research Database (NHIRD), birth certificate registry and death certificate registry] were linked in this study. A total of 10 236 offspring of mothers with PD were recruited, together with a comparison cohort of 81 888 births matched with the affected women in terms of maternal age and year of delivery. Each child was traced for 5 years from delivery between 2001 and 2003 until the end of 2008 to determine mortality during preschool years.

During preschool years, 98 (0.96%) deaths were identified among the offspring of mothers with PD and 470 (0.57%) children in the comparison cohort died. For children up to 5 years old, exposure to maternal PD was independently associated with a 1.47-fold [95% confidence interval (CI) 1.16–1.87] increased mortality risk, after adjusting for family income, urbanization level and the characteristics of mother, father and infant. The risk of death by unnatural causes was even higher (about 2.23 times the risk, 95% CI 1.34–3.70) among exposed offspring.

PD places preschool children at significantly increased risk of mortality, especially from unnatural causes of death.