Final answer:
Anti-D antibodies can prevent the hemolysis of foetal RBCs by binding and inactivating the fetal Rh antigens before they stimulate an immune response in the mother. These external antibodies are not identical to the maternal antibodies produced after exposure to the fetal Rh-positive blood during childbirth.
Step-by-step explanation:
The reason that Anti-D antibodies can prevent the hemolysis of foetal RBCs is because they bind and inactivate the fetal Rh antigens before they stimulate an immune response in the mother. These antibodies are introduced to the mother, typically through an injection, and they can prevent the mother's immune system from producing antibodies that would target and destroy the fetal red blood cells. It's important to note that these Anti-D antibodies are not identical to the maternal antibodies. The maternal antibodies are produced after exposure to the fetal Rh-positive blood during childbirth, whereas the Anti-D antibodies are introduced from an external source to prevent the immune response.