I agree that a belt in the blue colour would have looked better and united the top and skirt into an outfit. I don't mind the buckle though, because it sort of matches the style of the earrings.
In general terms, it's not really what I would describe as a maternity outfit. It's unusual for a pregnant woman to be drawing attention to her waist, which that belt does.
I sort of feel that the belt WAS actually meant to unite the skirt and top more already, but less in terms of colour and more in terms of fabric. That said, I still feel it missed the mark. As someone else posted, I'm thinking that perhaps the she didn't fit in the original top meant to go with the skirt - as all of us who are/have been pregnant have experienced. Perhaps this is the top they chose as a stand-in.