We chose not to have kids, so this one comes from the heart. Here are some extra notes:
Alternatives to "Mind your own business" from the rudest to the politest
My sex life and fertility status are private
You ask this every time we meet. Tell you what, when something changes, I'll let you know
Why do you need to know?
I don't know. So, what's new with you?
When the time is right. So, seen any good films recently?
If you want to opt for schooling them:
About 10% to 15% of Malaysian couples have fertility issues. Therefore, that question is considered rude/insensitive.
If you want to communicate openly
Statement of emotion
"I don't know. And frankly, I dread this question. It spoils parties for me, and holidays."
Block their arguing
"I'm not discussing it anymore."
Direct to action/new behaviour
"Please, don't ask me again. Don't talk to me about it."
"So, what's new with you?"
Enforce the boundary by walking away if they persist.