Influence of prenatal and postnatal growth on intellectual functioning in school-aged children

Abstract

Objective: To assess the relative influence of size at birth, infant growth, and late postnatal growth on intellectual functioning at 9 years of age. Design: A follow-up, cross-sectional study. Setting: Three districts in Khon Kaen province, northeast Thailand. Participants: A total of 560 children, or 92% of former participants of a trial of iron and/or zinc supplementation during infancy. Main Exposures: Prenatal (size at birth), early infancy (birth to 4 months), late infancy (4 months to 1 year), and late postnatal (1 to 9 years) growth. Multiplestage least squares analyses were used to generate uncorrelated residuals of postnatal growth. Main Outcome Measures: Intellectual functioning was measured at 9 years using the Wechsler Intelligence Scale for Children and the Raven's Colored Progressive Matrices (Pearson). Analyses included adjustment for maternal, household, and school characteristics. Results: Significant relationships were found between growth and IQ (Wechsler Intelligence Scale for children, third edition, Thai version), but only up to 1 year of age; overall, growth was not related to the Raven's Colored Progressive Matrices. The strongest and most consistent relationships were with length (birth, early infancy, and late infancy); for weight, only early infancy gain was consistently related to IQ. Head circumference at birth was not collected routinely; head circumference at 4 months (but not head circumference growth thereafter) was related to IQ. Late postnatal growth was not associated with any outcome. Conclusion: Physical growth in early infancy (and, to a lesser extent, physical growth in late infancy and at birth) is associated with IQ at 9 years of age. Early infancy may be a critical window for human development. © 2012 American Medical Association.