Early Onset and Increasing Disparities in Neurocognitive Delays From Birth to Age 6 in Children from Low Socioeconomic Backgrounds

Importance: The relevance of socioeconomic conditions to neurocognitive function in children is increasingly emphasized in the current discourse; however, a comprehensive body of knowledge on this is lacking. Objective To analyze the complex interplay between socioeconomic backgrounds and neurocognitive developmental achievements by investigating the temporal dynamics of these associations from birth to 6 years of age. Design: A retrospective cohort study over a 6-year period. Setting: Population-based data from the National Health Insurance Service, and integrated data from the National Health Screening Program for Infants and Children. Participants: Children born between 2009 and 2011 in Korea without neurocognitive delays with potential developmental implications. Exposures: Economic status at birth, categorized into three levels based on the amount of insurance copayment: <25th percentile as low, 25-75th percentile as intermediate, and > 75th percentile as high status. Main Outcomes and Measures: Overall judgement and six domains of neurocognitive development at 66–71 months of age, analyzed using the Korean Developmental Screening Test, to assess gross and fine motor function, cognition, language, sociality, and self-care. The secondary outcome was to determine when neurocognitive outcomes began after birth and how these differences evolved over time. Results Among 276 167 individuals (49.2% males), 66 325 had low status, 138 980 intermediate, and 60 862 high. Overall, neurocognitive developmental delays observed across all developmental domains were more prevalent in the low-status group than in the high-status group (adjusted odds ratio, 1.328; 95% confidence interval, 1.105–1.597). Interestingly, disparities in neurocognitive development according to these statuses became apparent as early as 2 years of age, with the gap tending to widen over time (interaction, P  < 0.001). Notably, the cognition and language domains exhibited the most substantial disparities between the socioeconomic levels. These disparities persisted in the subgroup analyses of sex, birth weight, head circumference, birth data, and breastfeeding variables. Conclusions and Relevance: Low SES was significantly associated with an increased risk of adverse neurocognitive developmental outcomes in preschool children, particularly those affecting the cognitive and language domains. These differences manifested in early childhood and tended to widen over time. Therefore, proactive interventions at a young age are essential to mitigate these disparities.