I cycled everyday until I was 40 weeks pregnant. It kept me fit, and was easier on my body then walking. I had to change from my racer at about 35 weeks though. It is just a choice thing, there are enough medical arguments either way- it just depends on the opinion of the person you happen to speak to. My MW really supported it. In terms of falling off etc- I did change my commute route- began using a slightly longer but much quieter way to work because I wanted to reduce the risks of an accident as much as possible. The thing is as soon as baby is old enough I will cycle with her on the back of my bike, and I can't really see the difference. If you want to cycle with babe then might as well begin when they are tucked up in utero! PS- she was born 2 months ago, a whopping 9 pounder and is perfectly happy and healthy- no strange head shape where her head was squeezed by my peddaling legs or other adverse impact!!! :P