Our daughter had this test as well for the first time when she was three months old.  Roberta is right on the money as to what the test entails.  It shows the urologist where the urethrovaginal sinus connects.  In layman’s terms:  it shows them where the urethra (tube where the urine comes out of the bladder and exits the body) connects to the vagina.  In some CAH girls they are connected.  To help you picture this in your mind better, imagine if you will the letter "y".  Do you see on the letter where the short arm is?  Imagine that the short line on the left of the letter is the vagina and the long line on the right of the letter is the urethra.  Where the "y" connects is different in every girl.  The lower it connects the better.

Our daughter was not put asleep for this procedure by the doctors in Phoenix.  The second time she had this procedure, a cystoscopy was used instead (for a different reason).  She was put under by a highly skilled team of physicians (Endocrinologist and Urologists) that came recommended by the CARES Foundation.org. and a CARES family that had also used the same team.  There was much less crying (none) and the urologist was as concerned for our daughter as we were.  It was well worth making a trip out of state for.  Please research with CARES before you chose a pediatric urologist. 

This test will be somewhat uncomfortable for her because of the catheter.  You may want to bring some comfort items such as a favorite blankie, pacifier, teddy bear, etc.

Good luck,

Adina