what's the best way to respond to the "when are you going to have kids" question?

Taneesha
So my sister is a bitch. Totally competitive and just an all around terrible person. 
She uses me as an emotional punching bag. Whenever she's not happy in her life she feels the need to call me up and berate me for whatever reason. It's really pathetic and I've stopped talking to her. Because of this I rarely talk to her and I only see her during family dinners. 
My husband and I got married in July but couldn't start ttc until January because of zika. She hosted Christmas dinner and asked us when we going to start trying. Thankfully I had zika as a reason why we weren't having babies yet. She argued that it wasn't a big deal and I argued that zika is a major deal and I want to limit as many risks as possible. 
Anyways, now we're trying and I can no longer use zika as an excuse so I'm looking for a witty response that will relieve tension but also let her know that I don't want to talk about my sex life with someone I see every 4 months in hopes and in front of people that I don't care about.....like her mother in law (who was at the Christmas dinner) so that she will not ask again. 
So what's your go to "it's none of your business" comment?