A girlfriend is throwing me a shower with about 10-12 girls. Another friend who is more my husband's friend is offering to throw us a co-ed party--I don't think she used the word shower, more like party or celebration. I'll tell her not to call it a shower. If she asks, would it be better not to put registry information on the party invite for the co-ed party since it's not a "shower"? I've been to these types of things and people bring gifts anyway; considering that, would it be bad for me to invite couples where the girl was already invited to my all-girls shower? I would think they would just know not to bring a gift to the "party," but I'd hate for anyone to think they should bring a second gift. The social circles kind of overlap so that's why I would invite couples where I already invited the girl to my shower (i.e. the husband is friends with my husband).
Re: Multiple showers
And I agree- people should NOT be invited to two gift-giving events for you.
the other option would be to only invite them to the co-Ed party.
I feel etiquette is important because it's really about taking your guests comfort into consideration and not being rude. But there are situations where it just doesn't always apply. or where going against the tried and true etiquette rules is actually what makes your guests happy.
I agree with the reply above that it's a situation where knowing your friends may trump traditional etiquette.
I certainly don't live to attend baby showers, but I do have a number of friends for whom I would attend both of the showers you describe. I rarely think it's appropriate for someone to be invited to 2 showers, but this is one of the possible exceptions.