how to handle nosy nellies

Katie
This girl I am casually friendly with (her BF plays hockey with my husband) asks me every 3 months "when we're going to start trying" and I want to jab her in the throat. 
I'm not close enough with her to even remotely go into details about my private life (PCOS and using fertility meds) so what should I say/do without killing her? Haha 
I always play it off like no big deal and say "oh I dunno" but it's quite upsetting.
Thanks girls 
Xo