Season of birth in autism: a fiction revisited.
The autism season-of-birth effect is a dead end—save your assessment time for real predictors.
01Research in Context
What this study did
Hatton et al. (1999) looked again at the old claim that kids with autism are born more often in March and August.
They re-checked earlier data using newer stats tools. The sample came from kids already given an autism or intellectual disability label.
What they found
No month stood out. The March and August spikes vanished when the numbers were cleaned up.
In plain words: season of birth does not predict autism.
How this fits with other research
da Silva Montenegro et al. (2020) folded this null result into a giant meta pool of over 20 000 cases. Their synthesis keeps the zero season signal, shifting the field toward gene and biomarker work.
Lyall et al. (2025) also hunt demographic clues but focus on race gaps in diagnosis, not birthdays. Together these papers show assessment research moving away from calendar trivia toward equity and biology.
Şimşek et al. (2021) and South et al. (2005) likewise report nulls in their own corners (VEGF levels and repetitive behavior splits). The theme: simple single-factor stories keep failing under close review.
Why it matters
You can stop charting birth months during intakes. Time saved can go to valid risk factors like family history or sleep patterns. Let the data kill the myth and keep your assessments focused on what really counts.
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02At a glance
03Original abstract
Variations of season of birth among autistic individuals were studied. The replicability of previously reported increases in birth rates in the months of March and August were examined in groups of individuals with autism or mental retardation (the comparison group). The sample was obtained from the Yale Child Study Center Developmental Disabilities Clinic and from the DSM-IV Autism/PDD field trial. Data were analyzed by applying the Jonckheere test of ordinal trend and the chi-square test, with Yates correction factor. With respect to March and August births, and with calculations based on the beginning and middle of the month, no significant seasonal effect was observed. Samples were subcategorized into verbal and mute groups, and again results failed to support the seasonality hypothesis.
Journal of autism and developmental disorders, 1999 · doi:10.1023/a:1023030911527