I have never been pregnant and raced, nor for that matter, been pregnant at all! However, I have had several friends who were bike riders who rode throughout most of the pregnancy (they did not race); most of them told me that their doctors told them to keep their heart rates below a certain level; so I would guess that racing might be out.

It makes sense that since you are supporting another little growing body that you would want some of the nutrients, blood, oxygen going there?

Anyway, I would ask a doctor - but as usual, hopefully, you know one that exercises a bit cause you could probably get some very divergent views from different doctors.