Greets!
Don't forget that air inflation is a light inflation, even the kind that floats on it's own, while liquid is a heavy inflation which just pulls people downward. Preg, however, is the idea of movement from within, not just the weight of something inside your body. Each one of the types have their own set of reactions, it's not just the shape of someones body before/during/after, but their reactions to the change that some people look at. Like me.
I like preg expansion because it has the widest (hah) set of reactions possible, as well it's easier to draw because (unless it's an unusual pic) pregnancy can only happen in one part of the body.
Also reminds me that I do way too many preg expansions. Now that I think of it, I think I only ever posted one other expansion type pic ever in Request and Sketch 1 (which was the Kagome demon bubble inflation)... O_o; I need to get more diverse with my work. So many processes neglected, so much time (wasted... ^^; ).