I stayed active but also within the 140 heart rate and was very careful not to get too hot. That meant no training for me. I rode my mountain bike slowly on quiet familiar roads up til my 7th month, when I couldn't pedal without hitting my belly. I also rode the trainer. Mostly I walked. A lot. I chose to take the slower pace because I didn't think I could live with myself if any harm came to my baby through my actions. In the last month and a half I ended up being put on bed rest on and off and a lot of whatever fitness I had maintained went out the door anyway. Ah well, I have a happy, healthy baby boy for my small personal sacrifices and no time to train to the speed I once had. I wouldn't change a thing. I'm patient and I'll get to race again. It's not like I'm some up and coming young star, I only raced for myself and right now I've got someone more important to take care of. It's not forever, just some days it seems that way.
I can't tell you what to do so I'm telling you what I did.
And wouldn't flying off your bike at 20mph approximate the forces of a car crash? I know I've broken bones, gotten concussions and gotten knocked out going slower than that (and on dirt)! For sure you can't insure that your crash won't involve your lower torso.