While many researches are still going on, it is difficult to say what causes autism with utmost surety. Parents continue to ponder upon what they may have done that caused this disorder in their baby, but they never come to a reasonable answer. Until now, it has been believed that autism is caused due to genetic factors. But recent researches indicate that a number of factors during prenatal stages may contribute to autism.

Many people from the medical field believe that the MMR vaccine can lead to development of autism, and some other vaccines containing a preservative named thimerosal, which contains mercury, can also lead to similar outcomes. Certain food items, like gluten and casein can also contribute to autism. Other factors include: intake of antidepressants during prenatal period, especially during the first trimester can harm the baby. The mother should consume a healthy and nutritious diet, as deficiency of certain critical elements like folic acid could prove a detrimental factor. Pregnancy complications such as low birth weight and anaemia, and children born to older parents are at higher risk of autism. Similarly, exposure to hazardous chemicals like insecticides and pesticides can harm the foetus and cause brain damage.