I can remember different ways I've been asked to undress at the doctor's, going back to school medical exams. There was mobile exam room which would visit our school every year, and we would go out to the parking lot, when called, for our physical. It was different each year, always a female doctor, the first year I remember she said, "You can take off everything, down to your underpants." (I wore briefs in those days.) I kept them on for the whole exam, until she checked the groin area while I was lying on the table and she pulled them down a little so she could feel underneath. Then the other time I remember, she said, "You can take off everything, except your socks." So, I was naked, except for socks, for the whole exam that time. I actually felt more exposed with the socks on than I did other times when I was totally naked.
I've also had medical exams in various countries around the world. In South Africa I was asked to undress gradually, first remove shirt, then remove trousers, then finally remove underwear. Each time just what was needed for that part of the exam. I suppose this was for modesty, but it was after I was totally naked that the nurse, and then the receptionist, came in a couple times with paperwork. So, timing didn't work out as probably intended.
In France, I was asked to undress completely at the beginning, and I remained like that until the end. No gown.