The Incredible Shrinking Belly?

In the past several days, I've been noticing that my belly seems to be getting smaller, as opposed to bigger. Here we are this morning (15 1/2 wks):

Clearly there is something there, but this is about where I was at 11 1/2 weeks...should I be worried about this? Or just grateful? These are my size 4 pre-baby shorts and a size small shirt...it seems even smaller in person (the belly, not the clothes..) Hmm...