I agree that doctors are only there to provide the service of medical knowledge and expertise, and that the ultimate decision should remain exclusively with the mother (or whomever the pregnant patient is).

As for your question, I'm unsure how we would directly go about preventing doctors' bias from negatively influencing patients' decisions, without blatantly denying positions from doctors who hold certain biases (which I think would be wrong, to certain extents). However, I think that there are certain things we can do to help prevent certain biases; things like nationalizing the healthcare industry, guaranteeing universal healthcare, abolishing private healthcare, etc. would be positive means of assuring that any patient would have access to a wide range of healthcare options and opinions, without being hindered by costs, insurance coverages, religious medical institutions, etc.