Can someone give me information on parental ABO blood types and the different possible outcomes?

[emilyosu]

UPDATE: it was the most likely answer. Grandma was wrong, dad is B+.

I’m not sure where else to ask, and it looks like this might be my best bet! I was always under the impression that O+ and O+ would make another O+ but kiddo is apparently B+! From what I’ve read, that suggests that: one of us is a chimera, or has cis-ab or Bombay blood types. It’s unlikely baby is a chimera/absorbed a twin since in theory that twin would have also been O+. I suppose the simple answer would be that they got his results mixed up in the hospital but I’m not sure how likely that is.

None of this actually matters in the long run (I don’t think it does, anyway?) but I do find it fascinating. If anyone has any research regarding unexpected blood types, share it here!

Edit: yes, he is unquestionably by husband’s baby. I figured the most likely answer would be either my husband was wrong about his own blood type or there was a lab mixup. Definitely my baby, though, he’s my twin.

 

[chumleypm]

@emilyosu Another explanation could be that one of the parents remembered their blood type wrong.

 

[jenlousie]

@chumleypm I work in OB - this happens all the time and is the most common explanation.

 

[maria21mercedes]

@chumleypm Happened with me and my partner. Turns out his mom wasn't the most reliable source of decades old medical information...

 

[metbeimife1973]

@emilyosu Have your and your husband’s blood retested as well. My mom always thought she was B+ and my dad was O+. When I had my baby I joked about my son and I both getting an A+ on our tests. She had a big “Wait a minute…” moment I thought there was a decent chance she was a chimera based on some other health issues but it was just a boring mistake many years earlier when she had me. She’s A+ as well.

 

[damacri]

@metbeimife1973 Yeah I was always told I had A+ blood by my mom. Turns out both me and the baby are actually O+

 

[likeatree]

@damacri Same here. I found it really interesting how shocked I was, hilariously. Like it was somehow part of my identity. Might have been the pregnancy hormones though…

 

[samin2345]

@damacri Same here. My mom always told me I was AB and I’m actually O-

 

[niansboog]

@emilyosu As another person said, O+ and O+ can only make O+ or O-, barring the incredibly rare possibility of a spontaneous mutation in baby's DNA. I've got general biology higher education training but I don't specialise in blood or genetics so happy to be corrected by someone more knowledgeable about other rare possibilities.

Chimera (edit: chimerism in the baby wouldn't, chimerism in you detailed in comment below), cis AB and Bombay still wouldn't give baby B type blood in your scenario. If you're certain the biological parents are both O+, I'd be looking into lab mix ups.

It does matter if baby ever needs a blood transfusion (if baby is actually O+ they can't receive B+ blood) and it does matter if baby is a girl and has her own baby one day (if she's actually O- and her baby is a + type there's additional medical steps involved).