For this game, you will need scissors and a spool of ribbon. How much you need will depend on the number of guests you have (and how far along the mom-to-be is!)
Have the mom-to-be stand in the middle of the room. Each guest should examine her belly. Next, pass the scissors and the spool of ribbon around the room. Each guest should cut the amount of ribbon that they think will go around the belly of the mom-to-be. The person with the closest cut wins!
A small prize, perhaps wrapped with ribbon from the same spool, may be given to the winner.