The Disappearing Seasonality of Autism Conceptions In California

Background:  Autism prevalence has increased dramatically motivating research for causative agents.Numerous studies have attempted to explore seasonality of autism births. However, the seasonality of autism conceptions  are of greater scientific interest. Our study addresses this gap in research, in addition of making significant methodological contributions.

Objectives:  To assess if the conceptions of children with autism cluster temporally and whether such temporal clustering of autism conceptions is robust over time.

Methods:  We searched for excess risk of autism conceptions from 1992 to 2000 using case and control data from California, adaptive temporal windows and a one-dimensional scan statistic. We test for confounding by known risk factors in the cluster period using logistic regressions.

Results:  There is a consistent but decreasing seasonal pattern in the risk of autism conceptions in November for the first half of the study period. Temporal clustering of autism conceptions is not compositional with respect to known risk factors for autism such as socio-economic status.

Conclusions:  There is some evidence of seasonality in the risk of autism conceptions. The pattern of decreasing and disappearing risk suggests a possible change in the nature of the cases that comprise the autism caseload in California.