Autism and hormonal birth contol link needs to be studied

In religious organizations where large families are the norm and birth control is not used, there are practically no cases of autism. Why is this phenomenon still not being studied? The religious organization I personally belong to lives an average modern lifestyle, including vaccinating our children and being surrounded by the same chemicals and processed foods as anyone else. Only there is no birth control or alcohol use. And the lack of autistic children in our communities is glaring.