While I appreciate that everyone gets excited about babies, please stop asking if I'm pregnant or when we intend to start a family.
It's a private matter between a husband and a wife, and if there's something we want to share with you, we will. Otherwise, don't think it's your business, because it's not. I will lie to you, until I decide not to, no matter the circumstance.
In my opinion it is never okay to ask someone that question. Ever.