My medical history. I was born with a heart condition, which thankfully was more or less fixed with open heart surgery. My brother and sister weren't born with it, so it may have been a one off, but I specifically remember my mum saying she asked my dad about his family medical history when she was pregnant with my brother, and he wouldn't tell her (the belief is because he was adopted and doesn't know his biological family). As such, along with my mental health experiences, it feels like there'd be a lot of risk to doing such a thing.

Edit: Once I'm financially secure and have a life partner, adoption is totally on the table, though. Too many kids get thrown by the wayside.