Prevalence of autism according to maternal immigrant status and ethnic origin

Objective: To examine the rates of autism separately according to maternal immigrant status and ethnic origin in respect to the vitamin D insufficiency hypothesis. Method: Articles were identified by electronic searches. Studies were selected when they analysed autism rates according to maternal immigrant status and/or ethnic origin using multivariate techniques. Results: This review gave further support to the association between maternal immigrant status and an increased risk of autism. The relationship with ethnic origin was more complex. Although the crude rates did not differ, multivariate analyses taking into account confounding factors found that black ethnicity was associated with an increased risk for autism. The risk was highly significant when considering the strict definition of autistic disorders as opposed to the large definition of other pervasive developmental disorders. The risk was also very significant for autism associated with mental retardation. Conclusion: These results are consistent with the maternal vitamin D insufficiency hypothesis. Neurobiological studies are warranted to document the effect of maternal vitamin D insufficiency during pregnancy on the foetal brain and the window of vulnerability. This review stresses the importance of monitoring vitamin D levels in pregnant women, especially those who are immigrant, dark-skinned or veiled, and the urgency of randomized controlled trials.