The cause of neonatal haemolysis is the transfer of antibodies produced by the mother, directed against the baby's blood cells, into the baby's bloodstream.

The basis for the development of haemolytic disease is the serological conflict that occurs between mother and child, which is based on the mechanism of the mother producing immune-type antibodies that are directed against the child's blood cells.

These antibodies are produced by the mother's body because the baby's blood cells, in the case of serological incompatibility, contain an antigen that is not present in the mother's blood cells. The penetration of the produced antibodies into the baby's blood, via the placenta, causes the baby to destroy blood cells, leading to haemolytic disease.

Responsible for the development of haemolytic disease is the serological incompatibility within the Rh system, where Rh (+) means the possession of the D antigen and Rh (-) means the absence of this antigen, thus a mother with the Rh (-) system can produce antibodies against the blood cells of a child with the Rh (+) system.[1]