You will not be permitted to wear anything but a gown, so be prepared. Just wear a tampon, if you change it right before you go in, then it shouldn't be a problem. You can tell your doctor if you are concerned/embarassed, but I am sure you will not be the first woman to ever have the procedure while menstrating.As for the preparation. I never had a colonoscopy, only a sigmoidoscopy which does not require cleansing. I did however have a barium enema which I did have to do the cleansing. It was quite an ordeal. I was expecting to be sick as soon as I took it so I stuck close to the bathroom, but it took a few hours to work. Once it did though, I didn't stop, all through the night and even when I got to the hospital the next morning. It was a lot more than I excpected. I didn't sleep much that night though. I had never gone that much in my life and it was A LOT. Don't plan anything big for that night. hope it all goes well.