Why does Rh incompatibility need previous sensibilization but ABO doesn't?

[jaumzaum]

I was wondering why a Rh negative mom needs previous Rh sensibilization (either by previous transfusion or previous children Rh positive) to develop anti-Rh antibodies, but a O+ or O- mom is already expected to have anti-A/anti-B antibodies, even when she is having the first child?

Also, why is Rh incompatibility usually more dangerous than ABO?

 

[Astronuc]

I was wondering why a Rh negative mom needs previous Rh sensitization (either by previous transfusion or previous children Rh positive) to develop anti-Rh antibodies,

The Rh negative means the mother does not have the Rh factor, which is then a foreign protein to which the mother's body reacts. I am Rh+, my mom was Rh- (my dad is Rh+), and that started an ongoing issue for my siblings. I believe my brother had one transfusion, my sister two and my youngest brother 4 transfusions.

I don't believe it is correct for a mother O- or O+ to be expected to have anti-A or anti-B, but certainly if a baby is AO or BO, or AB, then the mother might develop anti-bodies. A and B proteins would be foreign to an OO mother, so her body might have an issue with AO or BO baby.

Also, why is Rh incompatibility usually more dangerous than ABO?

Is that correct? Both can be serious.

 

[jaumzaum]

I don't believe it is correct for a mother O- or O+ to be expected to have anti-A or anti-B, but certainly if a baby is AO or BO, or AB, then the mother might develop anti-bodies. A and B proteins would be foreign to an OO mother, so her body might have an issue with AO or BO baby.

The firstborn A+ of a mother O- can have ABO incompatibility, but it is not expected to have Rh incompatibility as she was not sensibilized before.

From Wikipedia: "In contrast to Rh disease, about half of the cases of ABO Hemolytic Disease occur in a firstborn baby and it does not become more severe after further pregnancies"

Is that correct? Both can be serious.

From what I read, yes.

 

[Tom.G]

I'm not a medical expert, but I had an acquaintance that died several year ago from an Rh reaction. Not pretty to see.

As I recall from looking into the problem:
1) The first infusion of blood with the wrong Rh factor causes the body to start creating antibodies. This is generally not a big problem
2) After this first exposure, the body continues to generate antibodies, enough for a substantial concentration in the blood.
3) A second exposure causes an immediate and massive response to the 'foreign' intruder from all those circulating antibodies.
4) The 'foreign' intruder is quickly broken down.
5) The breakdown products are quite toxic, especially to the liver.
6) The end result is the liver is destroyed. Being essential, the loss of which is lethal.

I'm sure other more knowledgable people here can correct/fill-in details.

 

[Godot_]

[...]
5) The breakdown products are quite toxic, especially to the liver.
6) The end result is the liver is destroyed. Being essential, the loss of which is lethal.
[...]

Up to there it's OK. But Bilirubin isn't hepatotoxic, it's neurotoxic. Death is a rather rare final effect of Rh-incompatibility reaction - blindness and brain damage, however are quite probable...
...unless there's good neonate care available (ICU and/or dialysis - the latter with knowledge about the neonate specifities of electrolyte balance...)