According to the sources, erythroblastosis fetalis is caused by a specific type of Rh incompatibility between an Rh-negative mother and an Rh-positive foetus . While the blood of the mother and foetus are well separated by the placenta during the first pregnancy, exposure can occur during the delivery of the first child . This causes the mother to prepare antibodies against the Rh antigen in her blood . In subsequent pregnancies, these maternal antibodies can leak into the foetal blood (if the foetus is Rh-positive, often inherited from an Rh-positive father) and destroy the foetal RBCs, leading to severe anaemia, jaundice, or death . This condition can be prevented by administering anti-Rh antibodies to the mother immediately after the first delivery . Mastering these physiological mechanisms is a high-priority strategy, as NCERT textbooks serve as the primary source for approximately 95% of NEET Biology questions .