Have you measured your belly?
I just measured my belly the other day, for the fun of it - at about 38 weeks. I figured this is one time when I really don't care what the measuring tape says, so I might as well go for it! :) Over the fullest point, it's 42 inches, which is an increase of about 10 inches for me. (105cm, up 25cm, if my math is correct.) People generally say I don't look very big at all, but I think it's partly because I have a bigger frame and full bust (also about 42 inches), which makes the tummy look a little smaller in proportion.
So what's your tummy at? Anyone feel like sharing? :)