Re: What comprises "unnecessary" prenatal care?
It's ultimately what you feel comfortable with and want done. It's not (or shouldn't be!) up to your care provider what tests you do.
I would likely want to do a urine dip (and depending on that I would decide on the GD test, ie. if I was spilling protein, I'd want the GD test done, kwim?), check blood pressure and baby's heartrate, and do the 20wk u/s (not for gender, but for checking baby and placenta). I have done the GBS swab, as their "policy" is to treat with antibiotics if there's a positive result or if there's no testing done.
I am uncomfortable doing paps during pregnancy, so I decline that whole thing - which would mean I'm also declining the STD screening. No HIV testing done either.
I decline any vaginal exams until very late in the pregnancy, or during labor - with Levi I had one done at 41wks, IIRC, and then not until laboring.
For me, it is important that I do bloodwork at each appt - I get that "big draw" done at the beginning of pregnancy, for an idea of where my levels are starting, and I get my platelets and iron levels checked at each appt thereafter.
This is because I tend to have low iron during pregnancy, and because of my ITP we need to keep an eye on my platelets. Oh, and because of the platelet issues, I did have transfusions during labor/delivery with DS2 and DS3, and have had pitocin shots after each vaginal birth.