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 Were Identified from 1990 Through 2008 in Databases of the California Dept. of Devmtl. Serv., Which Coordinates Serv. for People with Devmtl. Disord.. the Outcome in This Anal. Was Autism Diagnosed before the Child's Sixth Birth Date. the Main Ind. Variables Were Month of Conception and Season of Conception . Multivariate Logistic Regression Models Were Used to Estim. Odds Ratios with Their 95% Confidence Intervals for Autism by Month of Conception. Results: Children Conceived in December , January , February , or March Had Higher Risk of Developing Autism Compared with Those Conceived in July. Conception in the Winter Season Was Assoc. with A 6% Increased Risk Compared with Summer. Conclusions: Higher Risks for Autism among Those Conceived in Winter Months Suggest the Presence of Environ. Causes of Autism That Vary by Season.
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