@ElizaBennett - I think you're right about pregnancy. I was able to do a pretty intense yoga workout while I was pregnant but there were a lot of poses I couldn't do just because of the weight of the belly.
If you're interested in yoga for weight loss, gentle yoga is only going to be helpful if you're just getting started and haven't been active. It's a great place to start getting off your couch. After a few weeks or months, once you're loosened up and more comfortable with moving around, you'll want to "graduate" to a more advanced class (some places call this "power yoga" or something similar) and really get moving.