I actually rode a bike when I was pregnant once, about 24 years ago. I didn't know it at the time but I was pregnant with twins and had my two-year-old in a child backpack. Not very smart, actually but I only went a few blocks to the library.

I'm sure you're much more fit than I was but I would be concerned about balance. As you get bigger, it's hard enough to stay balanced on your feet, let alone on a bike, mainly because you get big faster than your body can sometimes adjust, especially in the third trimester. So I do think it would be a good idea to ride a bike on which you feel very stable. Exercising while you're pregnant is a good thing but you do have to be careful and listen to your body.

Congratulations!