I have never had to have one. But if it doesnt sit right with you, regardless of whether its hospital policy, then refuse the appt, and you have every right to do that if thats what you want to do. They cannot refuse you treatment if it isnt done, they cannot bully you into having the appt either.
And do not feel bad about your weight, or your bmi. And dont worry about that right now. You can carry this bub to term, and you can deliver this bub. xo