For my sister's first, it was around Christmas that she wanted to tell the family, so she bought us each a shirt that said "World's Greatest" grandma, grandpa and aunt and made us open those gifts at the same time. We were puzzled for like .02 seconds, then we all squealed with delight. It was really fun. Then we all wore the T-shirts to the hospital when the baby was born--we didn't even plan that, we just were each so excited to become an aunt, grandma, and grandpa. It made for really cute pics.
If your pregnant now, Christmas is probably too late, but maybe someone's birthday or anniversary is coming up?
Congratulations!!!!! :-)