Make up a set of blank bingo cards (it's easy to find a printable version online).
Pass them out to the guests before the gifts are opened, and have them fill in the squares with the kinds of gifts they think the parents-to-be will receive.
Each square must have a different item in it.
As each gift is opened, if a guest has that item in one of her squares, she puts an X over it.
Whenever a guest ends up with a complete row of X's, she calls out "Baby Bingo!" and wins a small prize.
This keeps all eyes on the parents-to-be as they opens gifts and is lots of fun.