For me, the easiest thing is just to have a one sentence answer that I say to any and all comments and I just repeat the same line and walk away after saying it. I find the short, curt responses work best at ending the conversation.

So for questions like "When is number 2 coming?" or "When will a little brother/sister be on the way?" etc... I might say:

"I don't know, we'll see"
or
"Whenever we choose."

Then immediately walk away or change the subject completely.