As the original poster it's good to see that there's been several responses to my question.
Your preferences seem to be split fairly evenly but, for me, I much prefer the Doctor to be female.
I often fantasize about seeing my wife in lesbian situations (even though she's absolutely straight) and a medical examination by another woman is a dream come true for me!
In my perfect scenario she would go for her medical examination and the Doctor would be an attractive female, around 35 years old. She would be accompanied by 2 female medical students, around 25 years old, and she would ask my wife if it was OK for them to take part in the examination as part of their training. She agrees.
She removes her dress and bra and they start by examining her breasts. the Doctor goes first and carries out a very thorough examination of her breasts and nipples. then the 2 students take their turn while the Doctor looks on and instructs them. My wife has extremely sensitive breasts and the examination goes on for a very long time. Soon she's getting extremely aroused as the 3 women caress and fondle her breasts. She battles to remain calm but feels herself slipping out of control - by the time they've finished with her she's nearly coming and there's a damp patch visible in the crotch of her panties!
The breast exam over she gets on the table for the internal exam. She removes her panties and the crotch of her briefs is soaked with her cum much to the amusement of the Doctor and her 2 students. The exam starts with all 3 women taking turns to insert their fingers into her vagina. the exam is very thorough and intimate and of course my wife has to put up with it 3 times. She struggles desperately to remain calm but soon she's breathing heavily - as the relentless probing of her vagina continues she groans and flexes her wide spread legs.
The 3 women can see how aroused she is and decide to have a little fun with her. Taking turns to work her over they really turn the heat up on her by targeting her g-spot! They know exactly how to push her buttons and time and again she's taken to the brink of coming before they ease off, denying her relief. Eventually they tip her over the edge bringing her to a massive orgasm right there on the examination table!
Now what would I give to see that happen!