I was asked the other week by one of these goblins at work when my wife and I would be having another baby - a strange request anyway to know when my wife and I would be rawdogging it - but doesn't come from a place of care, it's just her being a nosey troll.
I find the best way to deal with these people is to embrace the embarrassment and uncomfortableness, and go into as much personal detail as possible (it doesn't matter if it's true or not), e.g.
"we're actually trying at the moment, we're at it like rabbits - been trying all these new positions, she loves it when <XYZ>, have you tried that, you really should! I can recommend you some videos if you want, but no seriously, she could barely walk the other day afterwards!"
The more gory details the better, I guarantee you she won't ask again!