It is a fact that pregnancy is very demanding on the soon-to-be mother's body and focus. It is a fact that a pregnant woman is far less likely be as productive and effective at work as if she's not pregnancy otherwise, well, because her body is already in overdrive 24 hours a day.
To me, even if your new boss is not being considerate, it is a correct business decision. If I were you, I'd really appreciate the move. If she had not made the adjustment, I'd probably ask to take less responsibilities. Of course, I'm not you and can not imagine what the effect of raging hormone would do to my brain.