Subtle differences in how babies grow during their first year may offer early clues about autism risk, according to new research tracking infant development from birth. The findings, published in Autism Research, suggest that both unusually small and unusually large head growth patterns are linked to a higher likelihood of autism, particularly when these patterns reflect broader physical growth rather than head size alone.
The study followed hundreds of children from birth through routine health checks in their first year of life, focusing on head circumference and height as markers of early development. Rather than relying on a single measurement, researchers examined how growth unfolded over time, capturing patterns that are often missed in standard check ups.
Infants whose head size consistently fell at the very low or very high ends of the growth chart were significantly more likely to later receive an autism diagnosis than those whose growth stayed within the typical range. The strongest associations were seen among babies at the most extreme ends, including those with very small or very large head measurements throughout infancy.
Importantly, the research found that head growth did not act in isolation. Head size and height were closely linked across the first year, and the increased autism risk was most pronounced when both followed similar atypical trajectories. This suggests that in some children, autism related differences may reflect wider patterns of physical development rather than changes limited to the brain alone.
Previous studies have often focused on rapid head growth as a potential early marker for autism, especially in babies born with average head size who then show accelerated growth. While this pattern was observed, it accounted for only a portion of the increased risk. Consistently small or large growth patterns appeared to carry a clearer association, highlighting the value of long term monitoring rather than one off measurements.
The research drew on detailed health records from routine infant clinics, where growth is measured at regular intervals during the first year. This allowed researchers to identify distinct growth trajectories and compare outcomes between children later diagnosed with autism and those who were not. By excluding premature births and focusing on children with complete data, the analysis aimed to provide a clearer picture of typical and atypical development.
The findings also help explain why earlier research has produced mixed results. Many children with autism show no unusual growth patterns at all, while others display changes that may be subtle or temporary. By looking at growth as a process rather than a snapshot, the study offers a more nuanced understanding of how physical development relates to neurodevelopmental outcomes.
While the authors stress that growth patterns alone cannot be used to diagnose autism, they suggest that combined measures of head size and height could contribute to earlier identification of higher risk groups. Earlier recognition may allow families and clinicians to monitor development more closely and access support sooner when needed.
The study adds to growing evidence that autism is biologically diverse, with different developmental pathways leading to similar behavioural outcomes. Understanding these early patterns may help refine screening approaches and deepen insight into how autism develops during the earliest stages of life.