My two favorites!! You should go with one of these!
The pregnancy fairy, I was at a party once with a very pregnant woman, she dressed like a fairy and carried around a pregnancy test and pointed it at people and said "Now you're pregnant too!"
It was hilarious, and really cute.
I have a quick and easy one for you.
When I was pregnant in October, my hubby and I both wore garbage bags. Mine had a sign that said, "I'm Hefty" and his had a sign that said, "And I'm Glad."