"The transition to fatherhood often involves both positive experiences and a range of new stresses," says Jing Zhou, PhD student at the Institute of Environmental Medicine, Karolinska Institutet, and co-first author of the paper. "Many cherish the intimate moments with their child, whilst at the same time the relationship with their partner may be affected and sleep quality may deteriorate, which can contribute to an increased risk of mental ill-health."

Study Tracks Over 1 Million Fathers Across Sweden

The researchers analyzed data from more than one million fathers whose children were born in Sweden between 2003 and 2021. Using linked national registers, they followed when men received new psychiatric diagnoses, beginning one year before pregnancy and continuing until the child reached one year of age.

Depression and Stress Diagnoses Increase After One Year

The findings show that psychiatric diagnoses became less common during pregnancy and in the early months after birth compared with the year before pregnancy. By one year after birth, diagnoses related to anxiety and substance use had returned to levels seen before pregnancy. In contrast, depression and stress-related disorders showed a clear increase. These diagnoses rose by more than 30 percent compared with rates before pregnancy.

"The delayed increase in depression was unexpected and underscores the need to pay attention to warning signs of mental ill-health in fathers long after the birth of their child," says Donghao Lu, senior lecturer and associate professor at the Institute of Environmental Medicine, Karolinska Institutet, and the paper's corresponding author.

Timing Support for Fathers' Mental Health

The researchers note that their results are based on clinical diagnoses, meaning men who did not seek care may not be included. Even so, the study highlights when fathers may be most vulnerable during early parenthood.

"By identifying periods of increased vulnerability, healthcare providers and other stakeholders can more easily offer support," says Jing Zhou. "Postnatal depression is often discussed for new mothers, but fathers' well-being is also important, both for themselves and for the whole family."

The study was conducted in collaboration with Sichuan University in China and Uppsala University in Sweden. It was funded by Karolinska Institutet's strategic research area in epidemiology and biostatistics, the Swedish Research Council and the European Research Council. The researchers report no conflicts of interest.