Rate of head growth decelerates and symptoms worsen in the second year of life in autism

Background: Longitudinal studies of bead circumference growth in infants later diagnosed with autism are needed to understand the accelerated bead growth in this disorder. Methods: We analyzed longitudinal head circumference data from birth to 3 years in 28 children later diagnosed with autism spectrum disorder on the basis of individual growth curve analyses using hierarchical linear models. Results: Head circumference Z scores relative to norms significantly increased in the autism sample from birth to 12months, but this pattern did not persist beyond 12 months. Rather, the rate of change in bead circumference from 12 to 36 months was not different from the normative sample. Conclusions. These results suggest that a period of exceptionally rapid bead growth occurs during the first year of life in autism; after 12 months of age, the rate of bead circumference growth decelerates relative to the rate during the first year of life, Studies of behavioral development in infants later diagnosed with autism suggest that the period of acceleration of bead growth precedes and overlaps with the onset of behavioral symptoms, and the period of deceleration coincides with a period of worsening of symptoms in the second year of life.