If you are going to use a backdrop, iron it! This is especially true if you do not actually own a professional backdrop and you are going to use a bed sheet or a piece of fabric. Nothing says amateur maternity portrait more than a wrinkly bed sheet taped to a wall with the mom-to-be standing about foot away like she's posing for a prison mug shot. If you can't iron it, steam it in your bathroom for an hour to get rid of the wrinkles. If you can't get rid of the wrinkles, don't use it at all. You will be better served using a wall or a doorway.
It is worth noting that some backdrops, such as the blue muslin below, are designed to remain wrinkled. It is possible to use to this to good effect. It is also possible to use drapery or wrinkles to create a textural backdrop, but in most cases wrinkled backdrops are just bad form.
When selecting a backdrop, you will want to be careful about the possibility of losing your subject. For example, in the photo to the left, replacing the wrinkled sheet with a black backdrop will hide any wrinkles the black fabric may have, but will also lose the detail from the back of the mom-to-be's head.
This is a very common error when photographing dark subjects on a black backdrop. This can be corrected with an additional hair light set behind the subject to outline the hair.
The same effect can also be used strategically, though it is rare. In the two examples below there is a huge difference in the contrast between photos of the same subject; a mom-to-be very pregnant with twins. The first photo, a traditional silhouette, is probably a better and more interesting photograph, but the second does succeed in honestly minimizing the size of the belly.
