I have this crazy phobia for doctors and hospitals, and I get anxiety from even potential health issues / complications and things going on with a body that are just not normal or simply different from usual. I think I would stress so much, it's just not worth it to me.
Also - I did always tell myself to try and reconsider it if I was 27 - 30 and in a healthy (longer) relationship and they wanted kids. But, my former partner got a vasectomy before he met me, so during the 7+ years we were dating, it was never something I had to think about.
I am turning 32 this year and single (2 years now), and I wouldn't want to have kids with someone whom I haven't been with for years. I don't see myself in a new long-term relationship anytime soon. If I'll ever find someone again, it'll be years from now before I would -maybe- want to have kids with someone, but I am pretty sure I don't even want to consider having kids between 36 - 40 (or older). Especially since the older you are, more complications may follow.
So, I figured it'd rather get with someone who already has kids. I wouldn't mind that they wouldn't be my own. Or, just not have kids in any way at all, of course. But to be honest, I would love to have kids in my life.