"What are you waiting on? When are you going to have another baby? Don't you want another one? "
STOP it!
Stop asking women who don't have children what they're waiting on. Stop asking women who 'only' have one child when they'll have another. For one it's none of your business and two how do you know they've not been trying? How do you know they're not dealing with medical issues preventing them from carrying a child? You don't! So just stop asking.
One of the hardest things to do is answer a question that you don't have the answer to and it makes one SCREAM!!!!!