Although we don't know exactly what causes autism, we do know that it is likely influenced by a combination of genetic and environmental factors. Autism can run in families. Parents may carry autism genes and pass them along to their children, even if the parent does not have autism. Sometimes, gene changes occur in the sperm, egg or embryo. These genes are believed to increase the risk for developing autism.
In addition, environmental factors may also play a role. Things like the age of the parent(s) at conception - older parents tend to have a higher risk of having a child with autism. Complications with pregnancy and birth can also be a contributing factor. Other factors that increase the risk include having multiples, extreme prematurity and low birth weight. It is also important to note that research has shown there is no correlation between childhood vaccinations and autism.
While many factors can contribute to the increased risk for developing autism, it has also been shown that mothers who take prenatal vitamins containing folic acid before and during pregnancy may be able to reduce these risks.