Objectives: To assess prospectively whether children with ASD identified from a cohort of high-risk infants (siblings of children with ASD) exhibit accelerated head growth relative to non-diagnosed high-risk infants and low-risk comparison infants (no family history of ASD).
Methods: Head circumference (HC) was measured prospectively on a total of 761 high-risk and 400 low-risk infants from 11 sites across North America and supplemented by data from health records (25% of total dataset). Analyses compared head growth between high-risk infants diagnosed with ASD at age 24 months (DSM-IV clinical best estimate based on developmental history and symptoms observed on the ADOS) to non-diagnosed high-risk and low risk infants. Growth trajectories were assessed using mixed longitudinal models, assessing change in HC as a function of time (linear growth) and time-squared (acceleration/deceleration), including sex as a fixed covariate, and height as a time-varying covariate.
Results: Mean HC at birth (model-based estimates) did not differ significantly between the three groups (p=0.08). However, there were significant differences between the ASD and both non-ASD groups in HC growth rate (growth rate 0.06 cm/month faster in ASD group compared to non-diagnosed high-risk and low-risk infants; p=.021 and p=.017, respectively), and in deceleration rate (deceleration rate 0.002 cm/month higher in ASD group; p=.018 and p=.021, respectively).
Conclusions: Prospectively measured head growth rates differentiate infants subsequently diagnosed with ASD from non-diagnosed high-risk and low-risk infants.