I support you 100% in talking with this inconsiderate boor, and also in empowering his patients to refuse "spectators". Perhaps the next time he appears in a patient's room, you can say, "Hello Dr. So and So, would you please introduce your student to Mrs. Mother to Be?" That way the patient will know that this person is someone whose presence is not required!
My dermatologist is a clinical professor at one of the Chicago medical schools
, and he frequently has students in the office with him. I have NEVER had a student walk in without the doctor expressly asking my permission, and I'm fully clothed! I can't imagine the indignity of having excess (and unnecessary) people present during an OB/GYN visit without my permission.
I agree that HIPAA may be the way to approach this. Especially with all the paranoia that exists about the legislation.
Good luck and thank you for advocating for your patients!