Background Longitudinal studies specifically looking at the transition into parenthood and changes in mental health in the general population are scarce. This study aimed to investigate the impact of transition into parenthood on mental health and psychological distress using longitudinal survey data.

Methods The analysis used three waves from the longitudinal Survey of Family, Income and Employment. Parenthood was classified as first time parent (first and only child <12 months at interview date), subsequent parent (child <12 months and other children in the family), existing parent (no children <12 months but other existing children in the family) and not a parent. We used fixed effects generalised linear modelling, controlling for all time-invariant and time-varying sources of confounding in a sample of 6670 adults within families.

Results After adjusting for confounding from time-varying partner status, area deprivation, labour force status and household income, those who became first time parents reported an increase in mental health (β 1.22, 95% CI −0.06 to 2.50; mean=83.8, SD=14.1) and a decrease in psychological distress (β −0.70 95% CI −1.10 to −0.29; mean=13.4, SD=5.0). Subsequent parents reported a decrease in psychological distress (β −0.60 95% CI −0.95 to −0.24).

Conclusions Our findings suggest that a transition into parenthood for the first time leads to changes in mental health and psychological distress. Understanding the relationship between becoming a parent and mental health outcomes is important given that parental mental health is integral to effective parenting.