I'm glad I decided to listen to the other reviews and order a smaller size, because otherwise I would have had to exchange it. I measured at the maximum Large measurement, and the medium is perfect. In fact, it's working so well I think I may even end up ordering a small in the future. I wish I would have used one of these after my first child! Only real negative is that it has a tendency to bunch up, ride up, and roll. If I do order another one, I think I'll go with the 9" instead of the 12".