Association of autistic spectrum disorder with season of birth and conception in a UK cohort.
Summer conception slightly lifts ASD odds in UK kids, but the calendar is only one small piece of a larger prenatal puzzle.
01Research in Context
What this study did
Van der Molen et al. (2010) tracked every baby in the ALSPAC UK birth cohort. They noted the month each child was conceived and later checked medical records for an autism diagnosis.
The team compared seasons to see if summer conceptions led to more ASD cases than winter conceptions.
What they found
Children conceived in summer had roughly double the chance of later ASD diagnosis.
The absolute risk still stayed small, but the seasonal pattern was clear across the cohort.
How this fits with other research
Spanoudis et al. (2011) used the same big-cohort method in California and found a flat 4.7 per 1000 ASD rate across seasons. The numbers look opposite, but the US study counted all births while the UK study split by season, so both can be true.
Sievers et al. (2020) links early birth, not season, to higher ASD odds in Brazil. This keeps the calendar idea alive: timing matters, yet the key trigger may be gestation length, not weather.
van Timmeren et al. (2016) saw no ASD rise after planned C-section or induced labor in a later British sample. Together the papers hint that events near birth change risk more than the month of conception itself.
Why it matters
You can reassure families that summer babies are still very unlikely to develop ASD. When you see a child born in spring, keep standard red flags in mind but do not over-screen. Use the finding as a conversation starter about other prenatal risks you can act on, like prematurity or maternal health.
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02At a glance
03Original abstract
PURPOSE: To examine the association between autistic spectrum disorder (ASD) and seasons of conception and birth in a UK birth cohort: Avon Longitudinal Study of Parents and Children (ALSPAC). METHODS: Seasons of conception and birth were compared in children with and without ASD with season grouped as follows: spring (March-May); summer (June-August); autumn (September-November) and winter (December-February). RESULTS: A total of 86 children with ASD were identified in the ALSPAC cohort giving a prevalence of ASD of 61.9 per 10,000. There was some evidence for an excess of children with ASD being conceived during the summer months with a rate per 1,000 conceptions of 9.5 in summer compared to 5.1, 4.6, 5.7 in spring, autumn and winter, respectively. A doubling of the odds was suggested for summer compared to autumn (Odds ratio 2.08 [1.18, 3.70]). In agreement with previous research, there was a corresponding peak in spring births. CONCLUSION: Conception during the summer months was associated with an over-representation of children with ASD in this UK birth cohort. There was also an association between ASD and spring births. Further investigation of seasonal influences on the aetiology of autism is required to identify possible factors in the environment, and their mechanisms and timings.
Autism research : official journal of the International Society for Autism Research, 2010 · doi:10.1002/aur.136