I don't know. It happens to me, too. My belly is huge and round and hard at the top but looks like nothing below the waist. I can feel my fundus just below my belly button so I know there's something there but it's not poking out. I can still wear my regular low rise pants. I wear a size 8 and had to go down to a size 4 in Old Navy to get a pair of low rise maternity pants that would stay up on me. They are still too big.
When I'm laying on my back first thing in the morning with a full bladder, I can feel the bump just below my belly button.