If one's throwing a themed baby shower, consider having the ultimate decoration - decorate your guests! Request guests attend dressed in appropriately for your type of shower. Attendees are sure to fully immerse themselves in your party!
You'll need to assess whether all guests would enjoy going to such extremes. If you believe guests would be up for this idea, include your 'dress code' request in invitations. Remind guests a week before via email. just to make sure noone forgets!
Showers needing a dress code
Having a dress code fits with most showers. Take these for example: