This is a bit heavier than the average grievance posted here, but like 10 years ago I found out I had a Balanced Translocation; which means a piece of one chromosome (the 20th? I can't remember) broke off and flew onto another one, resulting in me being unable to have kids. From what I understand, any attempt will likely result in a miscarriage, and if a child is born it may have health issues. Soooo, yeah.
But, honestly, I never wanted kids anyway; that's why it didn't bother me for so long. But, recently I was thinking that if I never knew about it, and ended up having one, what would have happened? Just a thought, though. The likelihood of that happening was slim.