Blood types

Do you have to know your own and your SO’s blood type BEFORE conceiving? I know I’m O, but no idea if + or - (I know it’s terrible that I don’t know my own blood type). My mom would know, but she passed when I was a teenager and I know my dad would be clueless.

I’m asking because I keep seeing posts about + moms miscarrying if the baby is - or something like that, unless they get a shot. But is it too late to get the shot once you’re already pregnant??