Here's a little tip for you:
Do not be mislead into thinking that you are entitled to half the mattress area while your wife is pregnant. A good idea would be to learn the art of perching on the very edge of the bed, clinging to the sheets. Perhaps create an elaborate strap system that holds you firmly in place to the side of the mattress?
And while you're creating elaborate strap systems, a pulley system to help your gigantic wife turn from side to side would also be ideal.
Good luck, and remember: she's not getting much sleep either, so it's all fair in the end.