Get 3 dolls or teddy bears (make the toys match the decor then give as a gift to the mom), about baby size and have a race to see who can properly diaper, dress in a onesie and swaddle. The mom to be is obviously one of the players and her mom and MIL or friends or however you want to do it.
Get a package of newborn or size 1 diapers and write messages on them with sharpies. It is really fun to use these diapers and remember the love and support you have when it is the 3rd night time diaper change and feeding and the new mom has not slept for a few weeks!
Get colored 3x5 cards or cut up cardstock and have guests write advice or a fond parenting memory, or expression of love or whatever and then put them in a photo holder book ( the little ones that just flip 1 picture at a time) It is a great decoration to the nursery if you get it to match the theme.
Trivia:
Who knew about the pregnancy first? (sometimes it is not the mom!)
How did dad find out?
Was this planned?
If there are already other Children, what were their initial reactions to the news? Did they change?
What were the symptoms that prompted a pregnancy test?
Any sickness? When?
Cravings? For what? Did dad have any?
Foods or smells to avoid?
Did anyone gain sympathy weight?
Due date?
Dr Estimated baby weight?
Gender?
Names that were considered.
Name chosen (if known)
Nursery theme
mom and dad birthdates and weights/ heights.
Get baby items that the new mom is going to need and play 'price it right' to see who can get the price closest to retail, not sale prices. New mom gets to keep everything.
Tylenol, breast pads, pacifier, a bottle, diaper cream, outlet plug covers, gripe water (the best stuff!) rattle or small toy, pkg of onesies, baby mittens, wash cloths, mylecon drops, you get the idea!
Take the labels off of baby food jars and pass them around. Let guests guess the food by tasting. Fruits and desserts work the best, but it is always fun to throw a few others in there, like mixed garden veggies with turkey!
Also, something my husband and I have done with our children is at their 1 month pictures, in addition to an individual picture and a new family picture we take one that is just mom, dad and new baby. It hangs in their rooms and is very special. Each pose is different.
Good luck and have fun!
I think this next one is gross, but so many people seem to love it: Take snack sized candy bars and melt them in the microwave onto a baby diaper and then have guests guess what it is.