Guys, don't confuse yourself...you don't need to tell anybody if 1. you are thinking to get pregnant 2. you are pregnant 3. due date of your child 4. childbirth.
Unless your spouse is pregnant and you are GOING to file and want to include a picture of your soon to be child then that's an option.
But you all already submitted your application...just imagine, everybody re-submitted evidence over evidence...another kaos.
Your child will be a US citizen so there is nothing to do there. Unless your child is not a US citizen then another story could be there but even so, one of you two are a US citizen, so will be only to do the correct paperwork which is different at ours.