AngHi Jackie,
I have CAH (since birth) and am 32 weeks pregnant with my second baby (another baby girl) I am on Dex and have had all the tests, genetic and prenatal that you mentioned. I am closely followed by a reproducive endocronologist and my first daughter DOES NOT have CAH and is perfectly healthy. Please feel free to ask me anything and I will try to get back to you.
In reference to the pregnancy tests for which I am sure you have your answer by now... With both pregnancies I got false negatives which were proven by HCG quantitative blood tests. When low HGC levels were indeed present - the test still implied NOT PREGNANT. Within a week they changed.
Good luck!