How can autism be diagnosed while pregnancy?

Confusing question: Are you referring to mom or baby ? If baby, there are some emerging studies that have detected patterns of genetic code alterations in autistic kids who have an affected sibling. These small insertions or deletions of genetic code may be amenable to prenatal diagnosis in a few years but would not pick up every case.At this point we are unable to define who or why a kid will develop the pattern.

It cannot be.: Autism appears to have multiple manifestations, and quite possibly, multiple causes. We are not at the stage where it can be diagnosed prenatally.