Autism Risk Abates in Later-Born Children

Published March 7, 2014 in Simons Foundation Autism Research Initiative

The risk of certain autism spectrum disorders is highest in firstborn children and declines in each additional sibling born to the same mother, reports a large Finnish study published in Paediatric and Perinatal Epidemiology. When the researchers looked at Asperger syndrome, pervasive developmental disordernot otherwise specified (PDD-NOS) and childhood autism, in which symptoms appear before the age of 3, as a group, they found that a diagnosis is most common in firstborns. The latter two conditions are now considered part of the autism diagnosis. When they looked at each diagnosis separately, the researchers found that the firstborn effect holds for Asperger and PDD-NOS, while second-born children are at the highest risk for childhood autism.

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