Rhesus Disease of the Newborn – Phase 2 Lecture Correction

At the end of today’s Hypersensitivity lecture, some one asked about Rhesus positive mothers having children.  I got a little confused and gave COMPLETELY THE WRONG ANSWER!  I thought the question was what if the mother has rhesus antibodies, and has a rhesus positive baby; the question being the baby dies, which is the answer I gave, and it’s the right answer, but not the answer to the question asked.  Thinking back, the question was, what if the mother is rhesus positive, and has a rhesus positive baby – well, if the mother is rhesus positive, any rhesus positive blood from baby 1 at parturition will not lead to antibody formation, because the mother is rhesus positive, thus will see the baby blood as native, not foreign.  Consequently, if baby 2 is rhesus positive, or rhesus negative, there will be no rhesus antibodies present, so reaction.

So.  Rhesus disease of the newborn does not happen in mothers who are rhesus positive, as they will never form anti-rhesus antibodies.  Rhesus disease of the newborn occurs in rhesus negative mothers who have a rhesus positive baby, blood mixes at parturition, anti-rhesus antibodies are made, and then subsequent rhesus positive fetuses are attacked by the antibodies.  The treatment is to give anti-rhesus antibodies to the rhesus negative mothers at parturition, to mop up any rhesus positive blood floating about, so the mother does not make anti-rhesus Abs, and thus has no memory cells to produce anti-rhesus in future pregnancies.

Sorry if I’ve mislead any of you – I was confused by the question!  Hopefully this will have cleared up any misunderstanding.

And yes – I’ve sent the lecture to the medical school to be put up on Blackboard.

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2 Comments on “Rhesus Disease of the Newborn – Phase 2 Lecture Correction”

  1. blood groups Says:

    is it even possible for the rhesus positive mother to have a rhesus negative baby? as don’t rhesus negative mother and rhesus positive father always have a rhesus posistive baby? or am I barking up the wrong tree?

    • dundeechest Says:

      Rhesus inheritance is complex, as there are over 30 antigens involved; however, RhD+ is dominant, and RhD- is recessive, so yes, a Rhesus positive mother should only ever have a Rhesus positive child.

      A RhD+ baby occurs in a RhD- mother when the father is RhD+, and it is this situation where mixing of blood at parturition is dangerous, as the RhD- mother will make the anti RhD Ab in response to the fetal blood. If a subsequent baby is RhD +’ve the Ab from the first parturition will pass though the placenta, attack the RhD+ fetus, and lead to erythroblastosis fetalis

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