If mother and foetus are ABO incompatible, her anti-A and or anti-B antibodies would rapidly destroy the foetus’ red cells before they could induce antibody formation.
An Rh negative woman can be sensitised and develop antibodies if she receives a blood transfusion of Rh positive blood.
In the past, Rhesus iso-immunisation was a great worry to every doctor who delivered babies. With modern treatment, it should no longer be seen. Unfortunately, that is not yet the case.
It is rare for the woman to be sensitised in her first pregnancy but one in 10 are sensitised by the second and the percentage becomes higher with each pregnancy. Previously, in six out of every 1000 deliveries, the child would be affected by Rhesus iso-immunisation.
Once the mother has formed these antibodies, they readily cross the placenta to enter the baby’s circulation and can destroy the baby’s red cells.
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