I love this technique for pregnancy, and I was keen to see if I could take a self portrait using it, so I gave it a try today. It's relatively simple to do (although it's admittedly a little more challenging as a self-portrait). Basically, you want to place a light behind and to the side of your subject so it's facing towards the camera in such a way that only a small amount of light is hitting your subject, effectively highlighting certain areas (like a big pregnant belly!).
Also, everyone keeps asking to see pictures of my belly and I have none, so I figured I'd better get started. There's only about 2 1/2 months to go!!