Crop tops are so hot right now.
The right crop top can be great for layering during your pregnancy and nursing. Now, I am not suggesting that you go all Lisa D'Amato, but if you do, more power to yah. Werk it gurl.
This is my attempt:
The top and shoes are vintage. The skirt is from +Zara; usually it's a maxi skirt but I've worn it up over my waist for this outfit.
Here's are some of my favorite pregnancy friendly crop tops:
American Apparel has some great wears in the way of crop top.
+H&M has some nice basic ones for sensible prices.