1) Gowns always look amazing in pictures.. and you can order from Amazon for last minute session. If you are doing a shorter dress, something that will give you a flattering silhouette works best. Stay away from busy designs, solid and simple is key. And go all out if you can...
2) Head pieces are a must!! There is something about the way pregnant mommies look with pretty head pieces. Floral, gold, silver, simple chain, whatever your heart desires.
3) Props: bringing baby shoes, the sonogram, and even a onesie can be fun to incorporate in the shoot.
4) Sticking to a relaxed and organic look so you aren't over powering the natural glow and beauty of your pregnancy is the way to go.