A: An invitation to a wedding shower comes with the expectation of an invitation to the wedding, too. A shower really should be an intimate gathering with your close friends and family, not a preview of your wedding reception. If you have too many people you want at your shower, you may need to trim your guest list, or else alter your wedding guest list to accommodate them all. Either way, make sure that all of your shower invitees will be invited to the big day. When someone offers to throw a shower for you, work with them on the guest list so there are no surprises.
Though occasionally a group of women (usually neighbors or friend's of the bride's mother) might throw a shower for a bride knowing they won't be invited to a small wedding, this is very rare and only works when the idea originates with the group of women who are offering to throw the shower, and they articulate that they understand they won't be invited to the wedding. Otherwise, it's a recipe for disaster.
Office showers are the rare exception when this rule doesn't apply. Make a mention to the organizers and at the office gathering that due to size you have to keep the wedding guest list small, but that you are so glad you had this opportunity to celebrate with them. —Anna Post, The Emily Post Institute