There is currently no known cause for autism spectrum disorder. However, scientists believe that some genetic and environmental aspects play a role in the cause of ASD. Genetically, it is believed that autism could be a genetic disorder or a genetic mutation in early stages of pregnancy. Environmentally speaking, there is some increased risk with advanced parent age, pregnancies spaced less than one year apart, and pregnancies with complications including low weight birth, multiple pregnancies (twins, triplets, etc.), and premature births.