Hiding Underwear From The Doctor

I have attended many gynecology exams with former girlfriends and now my wife. Every woman I have ever attended an exam with always hides her panties and bra under the rest of her her clothes. I am wondering if most of you women out there do the same thing and if so, why? I am particularly curious to know whether there are women out there that purposefully leave their bra and panties in plain sight for the doctor?

I think you'll find that there are at least 2 other threads on this, one dealing with GYN and the other a general discussion for any gender.