Faux Leather Leggings
For a fancier occasion, faux leather leggings are a good option. You can easily dress up a look without having to put on a dress that might not fit by adding faux leather leggings to the mix. Plus, you'll automatically look a little sassier, which can be a fun persona to undertake whether you're pregnant or not. 

Faux Leather Leggings, A Pea in the Pod, $135