Maybe someone can help me with some information.

I've been riding quite a bit although now I am 20 weeks pregnant. But I am afraid that last Sunday was my last ride. And I rode with all my gutts up the South Mountain. God! It makes me so sad! I've learned something new about riding and pregnancy. My coach and his wife, who is an avid rider and also a physio therapist for athlete women told me that I should stop. The reason is that pelvis and the lower back bone is shifting at this point. The saddle pushes right in between my pelvis. The structure of this bone is apparently not recoverable if I continue forcing it. I may end up with serious chronic lower back pains, which definitely nobody wants. If some doctor who does not know anything about cycling told me something like that, I would have dismissed it. But she is a "monster" rider and also a specialist, so she definitely scared me. I am very dissapointed and hope that she is wrong. Did anyone had an experience like this? How do I confirm her suggestion? I really don't want to learn it on my own bad experience.