The pregnancy will grow normally until birth of the child. After birth doctors have to check the blood group of the baby. If it is O positive like mother there is no problem but if it is O negative like father then mother has be injected with Anti-D within 72 hours of birth. When the placenta detaches child's blood enters mothers circulation. If child's blood is O positive like mother's there is no problem but if child's blood is O negative mother's immunity system considers child's blood as foreign bodies hence creates anti-bodies to destroy these foreign bodies. The anti-bodies remains in mother's body waiting for other same foreign bodies. If the next pregnancy is O negative these antibodies are ready to fight it believing they are foreign bodies. Anti-D injection within 72 hours of birth removes these anti-bodies in mother's body.
