Is there a method to reduce the chances of having an autistic child?

NO. We are just learning about risk factors associated with autism spectrum disorders. Autism is a neurodevelopmental disorder with many different factors. Important to discuss with a genetic counselor if there is any family history. Learn more about autism by reading a wonderful book, the thinking person's guide to autism.
Autism. We have no answers as to why autism is on the rise. We have no way of determining whether a baby will or will not have autism before birth.
Vitamins. Unfortunately, the cause of autism is still being determined. There seems to be a link to genetics and vitamin deficiencies. Taking prenatal vitamins before pregnancy and spacing out pregnancies seems to decrease the likelihood, but again, the actually cause or causes is still being worked out.