I've been generally lucky in my interactions with doctors. I've found most to be fairly clueless in dealing with the non-traditional - whatever that might be. Not generally condemning but more like such things never crossed their minds before. Once they make the adjustment, I've had decent experiences.
In fact, I was always asked about birth control even though I indicated on forms that I was partnered with a woman. I would reply "Lesbianism! It's very effective!" in the chirpiest, perkiest voice I could manage. Amused me, if no one else.
I also complained about how organization and language used in the forms did not easily allow me to clearly indicate that I was a lesbian and that I was in a LTR with a woman. And how to fill out the marriage status was a whole other irritating situation.
And poly folks have similar difficulties - I have seen life or domestic partner crop up on medical forms - but I have never seen a medical form capable of describing the complexities of poly arrangements. Hell, they don't reflect the complexities of just about everybody's life in some or another. It required some explanation of my answers on the form when I starting going to my current gynecologist because the form just couldn't convey that 1) at the time, long term relationship with a female partner, 2) several male sex partners and 3) yes, I wanted permanent birth control. To her credit, she was matter of fact once she wrapped her head around it.
The most positive experience I've had was with a nurse practioner who was getting my sexual history during an initial appointment. WHen I told her I was bisexual, she paused and then heartily said, "Good for you! More chances!" Cracked me up.