This problem arises as a result of the genetic transmission of Rhesus factor from parents to children. When a mother is Rh negative and the father is Rh positive there is a chance the baby will be Rhesus positive. There will be a 50% or a 100% chance of a baby being Rhesus positive depending on the genetic makeup of the father.
In Rh incompatibility the mother will develop Rh antibodies if there is blood to blood contact with her Rh positive baby. Mixing of maternal and baby blood may occur during birth. The rhesus factor in the baby’s blood will act as an antigen in the circulation of the mother, causing her to produce Rh factor antibodies. This does not usually affect the baby during the first pregnancy, however during subsequent pregnancies she will already possess antibodies to the Rh factor. This can result in the mother’s antibodies crossing the placenta and attacking the baby’s blood, leading to a condition called haemolytic disease of the newborn. Affected babies have a reduced oxygen carrying capacity of the blood and are jaundiced due to the presence of red cell breakdown products such as bilirubin.
This complication should now be prevented by the administration of an Anti D injection, given to the mother after the birth of every baby. These injected D antibodies quickly destroy (mop up) any Rhpositive baby cells in the mother’s blood. The result of this intervention is Rhpositive cells are not present in the maternal circulation for long enough to stimulate the mother’s immune system to produce antibodies to the Rhesus factor.