I lost 30 lbs while pregnant. The maternity clothes that fit when I was 18 weeks were hanging off every part of me except my belly by the time I was 39 weeks. Two weeks after Tristan was born, I was down 40 lbs from where I had been six months before he was conceived, and I had to buy smaller jeans because my pre-pregnancy jeans were two sizes too big.
I've put a little bit of that back on, but I'm still below my pre-pregnancy weight. Some of that is due to the fact that I've been off my thyroid medication for a couple months now because things got so crazy around here that I was forgetting to take it and now I have to wait to have some bloodwork done to determine my levels before my doctor will write me another script.
I'm giving some half-serious consideration to getting pregnant again to see if I can lose a bit more.