Not exactly true; there are other factors. Our son was born very premature, 2 lbs 12 oz. You could hold him in one hand. (He is a big strapping 13 year old now) They are finding that there is a higher rate of autism in preemies compared to normal births. 'Decades' ago, there is a good chance he would not have survived, thus there is a higher incident of autism simply because preemies are surviving instead of dying.
Thank you for taking the time to point this out. I don't think this is properly taken into consideration.