If you google 'baby shower invitation wording' you'll get a list of websites that will help. I've used
www.invitingsmiles.com to help me out in the past. I also printed the below poem on cardstock and placed them at each table setting; its a cute way to say thank you for coming.
I'm really glad that you could come
And help surprise my mother
sit down, relax, enjoy yourselves
and chat with one another
Sorry I can't be with you
to join in Mommy's shower
But I'm very busy you see
I'm growing more each hour
Though I'm not there to thank you
for the lovely gifts you've brought
my family is grateful
we appreciate the thought
I'll be arriving shortly
and I'm as happy as can be
so, after I've been home awhile
please come and visit me.