Head Growth Trajectories During the First Year of Life and Risk of Autism Spectrum Disorder.

Atypical infant head circumference (HC)-including increased rates of macrocephaly and microcephaly-has been linked to autism spectrum disorder (ASD). However, specific head growth trajectories associated with ASD remain poorly defined. This retrospective case-control study aimed to delineate these trajectories and examine their relationship to height. The study sample included 262 children diagnosed with ASD and 560 matched controls. Growth measures at 1, 2, 4, 6, 9, and 12 months of age were obtained from health clinics in southern Israel. The sample was classified into seven clusters based on HC patterns across these six time points, and associations with ASD were estimated using conditional logistic regression. Results demonstrated significant correlations between HC and height throughout the study period (Pearson correlation r = 0.44-0.55, p < 0.001), with stronger correlations in ASD (r = 0.50-0.67) compared to controls (r = 0.32-0.50). Children with consistently small or large HC exhibited the highest ASD likelihood (adjusted odds ratio [aOR] = 2.95, 95% CI = 1.88-4.94; and aOR = 3.17, 95% CI = 1.92-5.01, respectively), with the most extreme percentiles (0-5th and 95th-100th) showing the strongest associations (aOR = 9.53, 95% CI = 2.49-35.26; aOR = 6.51, 95% CI = 2.91-15.35, respectively). These associations were primarily driven by children with similar height trajectories (aOR = 7.71, 95% CI = 3.23-15.43; and aOR = 6.89, 95% CI = 2.99-13.26, respectively), indicating that atypical HC growth in ASD during infancy may reflect broader physiological growth dysregulation.