mine never popped out with either pregnancy
P.S. As a kid I always thought when the belly button popped it was a sign that the baby was ready - just like a turkey timer! haha! But if you've ever cooked a turkey, sometimes the bird is done before the timer pops! :)
Mine didn't either with my first pregnancy, although I have a deep belly button too, so that's probably part of it.
Funny you say that, my belly button did not pop out during my first pregnancy and during this one has not either.
I'm in my 30th week. I was told not everyones belly button pops out while pregnant and less likely for overweight.