Although I had a CVS test, which indicated my baby did not have CAH, it is not apparantly 100% foolproof.  The baby had to have blood tests 2 weeks after birth to ensure he did not have CAH -I was told earlier tests would not be totally reliable either.  I suppose the 1:4 chance of having another affected child is a pretty high incidence and newborn screening can give false positive readings too - although I am told this is quite rare.  I think it is therefore just a precaution!