Rhesus incompatibility

Rhesus is an RBC membrane surface antigen.  In normal conditions, it has little significance.  In pregnancy, it can present a problem.

When a Rh-ve mother carries a Rh+ve child in her first pregnancy, there is a danger that the child’s RBCs will cross the placenta and the mother will develop antibodies to the Rh antigen.

This will then cause a type III hypersensitivity, haemolytic reaction against the child’s RBCs.  However, this rarely causes problems in the first pregnancy, because this process takes time and the majority of sensitisation begins around the time of delivery.

However, it can (and will) present problems in future pregnancies, when the Rh-ve mother’s Antibody will attack the Rh+ve baby’s RBCs straight from the word go.  This will cause a haemolytic anaemia of the baby- causing jaundice, anaemia etc to an extreme degree.

Management during the first pregnancy (and then subsequent pregnancies) is to administer Anti-D antibodies (anti Rh antibodies).  The mechanism is not certain (you would think this would be the worst thing to do), but it seems to suppress the maternal production of Ab and thus the mother never becomes sensitised (the effect of the exogenous Ab is insignificant to the baby).

Management of an emergency (i.e. sensitised mother vs baby reaction) episode should be delivery (where possible), administer anti D to suppress the production of the maternal antibodies, and management of the baby once it has been delivered (i.e. manage jaundice (photodynamic therapy), give steroids for surfactant and blood for anaemia).

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