Head circumference at birth and school performance: a nationwide cohort study of 536,921 children

Background Early measures of cognitive function are of great public health interest. We aimed to estimate the association between head circumference at birth, a measure of cerebral size, and school performance. Methods We conducted a nationwide cohort study of all liveborn singletons in Denmark, 1997–2005. The association between birth head circumference z score and test scores in reading and mathematics from a nationwide mandatory computer-based school test program (7–16 years) was estimated by multivariable linear regression adjusted for potential confounders. Results The cohort included 536,921 children. Compared to normocephalic children, children with microcephaly [<−2 standard deviations (SD)] had lower mean reading scores: second grade: −0.08 SD (95% CI −0.10 to −0.06), eighth grade: −0.07 SD (95% CI −0.10 to −0.04). Macrocephaly (>+2 SD) was associated with higher scores. In normocephalic children, each SD increase in head circumference was associated with a 0.03 SD (95% CI 0.03 to 0.04) increase in mean reading scores. The results were similar across grades within both reading and mathematics. Conclusion Prenatal brain growth may be causally related to childhood school performance. The demonstrated differences are unlikely to be clinically relevant at the individual level but may be important at a public health level.