Month of conception and risk of autism
Ousseny Zerbo1, Ana-Maria Iosif, Lora Delwiche
1Department of Public Health Sciences, School of Medicine, University of California, Davis, CA 95616, USA. ozerbo@ucdavis.edu
Insights
Conceiving during winter months, particularly December through March, is linked to a higher risk of autism spectrum disorder (ASD). These findings suggest seasonal environmental factors may influence autism development.
Area of Science:
- Neurodevelopmental Disorders
- Environmental Epidemiology
- Perinatal Health
Background:
- Understanding the etiology of autism spectrum disorders (ASD) is crucial, as it remains largely obscure.
- Investigating the impact of season of conception offers potential insights into environmental influences on ASD risk.
Purpose of the Study:
- To determine if specific conception months or seasons are associated with an increased risk of autism spectrum disorders.
- To explore seasonal variations in environmental factors that may contribute to ASD etiology.
Main Methods:
- A large cohort study of 6,604,975 children born in California between 1990 and 2002.
- Autism cases (n=19,238) diagnosed before age six were identified using California Department of Developmental Services databases.
- Multivariate logistic regression models analyzed the association between month/season of conception and autism risk, calculating odds ratios (ORs) and 95% confidence intervals (CIs).
Main Results:
- Children conceived in December (OR=1.09), January (OR=1.08), February (OR=1.12), or March (OR=1.16) showed a higher risk of autism compared to those conceived in July.
- Conception during the winter season (December-February) was associated with a 6% increased risk of autism (OR=1.06) compared to summer conception.
Conclusions:
- The elevated risk of autism associated with winter conception suggests that seasonally varying environmental factors may play a role in ASD development.
- These findings highlight the potential importance of environmental exposures during specific seasons in the etiology of autism spectrum disorders.
Background:
Studies of season of birth or season of conception can provide clues about etiology. We investigated whether certain months or seasons of conception are associated with increased risk of autism spectrum disorders, for which etiology is particularly obscure.
Methods:
The study population comprises 6,604,975 children born from 1990 to 2002 in California. Autism cases (n = 19,238) were identified from 1990 through 2008 in databases of the California Department of Developmental Services, which coordinates services for people with developmental disorders. The outcome in this analysis was autism diagnosed before the child's sixth birth date. The main independent variables were month of conception and season of conception (winter, spring, summer, and fall). Multivariate logistic regression models were used to estimate odds ratios (ORs) with their 95% confidence intervals (CIs) for autism by month of conception.
Results:
Children conceived in December (OR = 1.09 [95% CI = 1.02-1.17]), January (1.08 [1.00-1.17]), February (1.12 [1.04-1.20]), or March (1.16 [1.08-1.24]) had higher risk of developing autism compared with those conceived in July. Conception in the winter season (December, January, and February) was associated with a 6% (OR = 1.06, 95% CI = 1.02-1.10) increased risk compared with summer.
Conclusions:
Higher risks for autism among those conceived in winter months suggest the presence of environmental causes of autism that vary by season.
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