Christmas card announcement

I am 7 1/2 weeks right now and will be almost 10 weeks when I send out Christmas cards. My husband and I haven't told our 3 children or any family and friends, except for a couple close friends that we are expecting our 4th child. I plan to announce it in our Christmas card (with cute pictures involving our other 3 children) 
 What do you all think? Please no rude comments. I'm just looking for opinions. :)