Association of relative age with medical consultations for developmental concerns: A nationwide birth cohort study in...

The relative age effect is associated with high rates of attention-deficit/hyperactivity disorder diagnosis in the youngest children in a classroom. However, it remains unclear whether relative age affects the earlier stage of initiating medical consultations for developmental and behavioral concerns before a diagnosis is confirmed.

We analyzed the Longitudinal Survey of Newborns in the 21st Century, a nationwide population-based birth cohort in Japan. We compared 23,423 January-born children (born in the relatively younger months of the academic year) with 23,592 July-born children (born in the relatively older months of the academic year). The primary outcome was caregiver-reported medical consultations for developmental and behavioral concerns between ages 7 and 12. The secondary outcome was caregiver-reported "restlessness" at age 9.

The prevalence rates of medical consultations were 6.0% and 5.2% for January- and July-born children, respectively. The adjusted risk difference (aRD) was 0.79 percentage points, and the adjusted risk ratio (aRR) was 1.18. This association was observed in both sexes but was statistically significant mainly in boys (aRR, 1.19). Caregivers were more likely to report January-born children as "restless" at age 9 (24.4% vs. 21.4%, aRR, 1.14).

In this Japanese cohort, being born in the relatively younger months of the academic year was significantly associated with a higher frequency of medical consultations for developmental concerns. The findings suggest that relative age may serve as a contextual factor in the process of seeking medical advice, although whether this reflects true differences in clinical need or misattribution of normal immaturity remains to be elucidated. Clinicians should consider relative age when evaluating children for developmental concerns.