My mother, my grandmother and I all have/had the same blood group, B Rh Neg which is fairly rare. My grandmother was a donor, but neither my mother nor I were ever able to be, mum because she had jaundice as a child and me because of the anaemia. I'm the only diabetic in the family.
A friend of mine who is currently expecting had the anti-D jab a few weeks back, they only discovered her problem this time round because a doctor decided to ask about blood groups and tested her and her partner. She's had a couple of miscarriages in the past and no-onhe knew why until now. she confidently expects to get through this time and is around 6 months at the moment, doing well.
I found out my bloood group back in the 80s because I asked and the doctor told me. I'd been tested as a child because of the rarity of my mother's blood group, they were hoping I could be a donor when I was old enough.