I do think there is a test that can tell. It just can't tell you how bad the Nf could be. I am 44 years old and thankfully have a mild case. Just have the birthmarks and raised nodules on my stomach.
Yes cvs test or a more accurate one at about 5 months is an amino. More precise but more risky. You can do invitro with pregenetic testing to make sure they don't have nf if that's what you are goin for.