Prenatal head circumference in autism spectrum disorder

Research has documented a phenomenon of early brain overgrowth in autism spectrum disorder (ASD). Although the most significant overgrowth seems to occur within the first few years of life, the exact timeline, clinical correlates, and relation to earlier brain development are not well understood. A growing body of research points to a prenatal origin, yet few studies have examined prenatal head circumference (HC) in children diagnosed with ASD. Previous investigations have been limited to comparing HC measurements at the second trimester, neglecting later points in gestation when critical regulatory and developmental processes may be going awry. In addition, these analyses may be influenced by biased normative data, as has been recently suggested by various research groups. Finally, the connection between prenatal HC and later developmental outcomes has yet to be explored. The current study sought to expand upon current literature by examining both second and third trimester prenatal HC measurements in children with ASD, as well as the rate of growth between trimesters. Additionally, the current study explored the relation between prenatal HC growth and later symptom severity. Examining HC later in gestation contributes to a more complete understanding of how and when brain growth dysregulation occurs in the development of ASD. Analyses indicated an unanticipated finding of significantly smaller mean standardized HC for ASD participants as compared to normative growth charts. In addition, second and third trimester HC measurements suggested an accelerated rate of neural growth for children who later developed ASD.