My son was diagnosed in utero. You can choose whether or not to have the blood test done for being a carrier, and I chose not to since we had no CF in the family and I didn't know much about it. My son's ultrasounds came back with a bright bowel, so that was the first red flag. I was tested for being a carrier and it came back positive, then my husband was tested and he came back positive. So, then I had an amnio done, and they tested specifically for CF and that came back positive. That's the order in which they did all the testing. Hope this helps.