Early-life pathways to inequalities in child mental health: evidence from eight birth cohorts

Background: Socioeconomic inequalities in children's emotional and behavioural problems are already present at school entry. We examined associations between early-life socioeconomic conditions and children's externalising and internalising problems and assessed whether early-life risk factors mediated these associations. Methods: We analysed harmonised individual participant data from eight birth cohorts within the EU Child Cohort Network. Maternal educational level during pregnancy was used as an indicator of early-life socioeconomic conditions (SECs). Scores of children's externalising and internalising problems around school entry age were used as the outcome variables. Inequalities were quantified using the Slope Index of Inequality which captures the difference in prevalence of problems between children from highest and lowest SECs. Mediation analysis was used to assess the mediating role of five early-life risk factors: maternal smoking during pregnancy, gestational age, small for gestational age, postpartum depression and breastfeeding. Results: Inequalities in externalising and internalising problems by SECs were consistent across cohorts: Children of mothers with low educational level had on average a 12 and 11 percentage point increased prevalence of externalising and internalising problems respectively. Early-life factors explained around 8% (DNBC, Denmark) to 54% (INMA, Spain) of the inequality in externalising problems and 7% (ELFE, France) to 25% (ALSPAC, UK) in internalising problems. Conclusions: Children from lower SECs consistently had a higher prevalence of both externalising and internalising problems around school entry age. These inequalities were partly mediated by early-life factors. Public health interventions in pregnancy and the preschool period are critical to address the early emergence of inequalities in children's mental health.