I agree, At 13 weeks you can feel a very tight area, from a little more than a inch under your belly button to your pubic bone. I think the only way I am noticable is from all the bloating.

I think in general you dont start to show to others till after 20 weeks.(Thats about the time people send us wedding invites, and I cant find suitable clothes to wear.lol. Thats happened a couple of times now.)