Is it bad to shave the hairs off your belly if you are pregnant?

Ok to do. Cutting or shaving hairs anywhere on the body is ok (as along as one does not create a skin infection by shaving too closely or getting too many ingrown hairs). Since the portion of the hair that is outside of the hair follicle is not alive, one's body does not know the hair has been cut (so cutting hair does not affect the pregnancy or anything else inside the body).
No, but be careful. Inadvertent shaving nicks or cuts can cause a rash, or infection during a time (pregnancy) when your increased vascularity can spread the infection to the blood stream very rapidly.