What is the biggest predictor of autism?

Autism, or autism spectrum disorder, has no single cause, and researchers describe it as influenced by a combination of genetic and early developmental factors rather than one predictor. The strongest and most consistently reported risk factor in large studies is familial and genetic influence. Having a sibling or parent who is autistic is associated with higher likelihood, and twin and family studies suggest many common and rare genetic variants contribute. Other factors that have been studied include advanced parental age at conception, certain prenatal conditions, very preterm birth, and exposure to specific medications during pregnancy, but none of these alone predicts autism and most children with these factors are not autistic. There is no evidence that vaccines cause autism. Early developmental differences in social communication and patterns of behavior are how autism is identified, typically through developmental screening. If you have concerns about a child or yourself, a pediatrician, developmental specialist, or psychologist can provide screening and discuss family history and next steps, and early support is associated with better outcomes.