My daughter had this done the first week of her life.  It was the last test before they let her go home.  I know they are checking to see if any urine is refluxing into the kidney and or vagina.  I was not alowed to go with her and I regret this.  I wish I had insisted, but I was overwhelmed and sleep deprived from living in the hospital and ronald mcdonald house.  It was supposed to take 20 minutes, but after an hour, the nurse called to see what was going on.  Later I read her medical report and they had a hard time putting the catheter in and they decided to explore in her rectum-why, I don’t know.  When she came back she was upset to say the least.  I would do all I could to remain with your daughter for the test.  If you are watching, the team of health care people will do their best to minimize discomfort, and keep you the parent calm.  Also most doctors are delighted to get a rare glimpse of what CAH and all that goes with it looks like and your baby becomes something for students and first year residents to get a look at.  This test probably is necessary, but why not research if you haven’t all ready, and make sure this is the best option at this time.  I’m sure other people will give you some responses.