Head Growth Trajectories During the First Year of Life and Risk of Autism Spectrum Disorder.
Head size that stays in the top or bottom 5 % through the first year carries a 6–9 fold jump in autism risk.
01Research in Context
What this study did
Doctors tracked head size every month for 1,000 healthy babies. They used regular tape measures at well-baby visits.
They waited to see which children later got an autism diagnosis. Then they asked: did head size in year one predict the outcome?
What they found
Babies whose heads stayed in the bottom 5 % or top 5 % had 6–9 times higher odds of later autism. The middle 90 % showed no extra risk.
Both very small and very large heads mattered. Risk rose the further the head size sat from average.
How this fits with other research
Geurts et al. (2008) saw the same pattern in baby brothers and sisters of autistic children. Their small 2008 study now gets strong back-up in a general sample.
Cederlund et al. (2014) looked only at preschoolers who already had autism. They found big heads in just 3 %, matching any daycare class. Timing explains the clash: Mats missed the first-year growth spurt that Rewaa caught.
Stewart et al. (2018) found no link when they measured head size before birth. Prenatal scans and postnatal tape measures tell different stories; the useful window starts after birth.
Why it matters
You already measure head circumference at 2, 4, 6, 9 and 12 month visits. Circle any baby who lands below the 5th or above the 95th percentile two visits in a row. Flag the chart for the pediatrician and tell parents you will watch communication milestones a little closer. No extra tools, no cost—just use the data you collect anyway.
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02At a glance
03Original abstract
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.
Autism research : official journal of the International Society for Autism Research, 2026 · doi:10.1016/j.earlhumdev.2020.105224