Question

So this is what I understood about the disease by researching about it When a Rh-ve mother has a Rh+ve baby in her womb, The placenta prevents mixing of fetal and maternal blood preventing antigen detection by her immune system.There are no pre-made antibodies that can attack the fetal RBCs to kill themAt the time of birth, the placenta breaks thereby exposing the fetal RBCs to her immune systemThe WBCs get sensitised and begin antibody formation which takes atleast 6 monthsThe first baby is born safelyIn the event a second Rh+ve baby is conceived, the antibodies aleady present in the blood

cross the placenta and destroy the fetal RBCs killing it.(secondary immune response)To prevent this an injection of Rh antibodies is given to the mother after first birth which
destroys all fetal RBCs before they sensitise the immune system preventing secondary immune
response. My Question is Why does this happen only with the Rh antigen? I know many people whose mothers have B+ve/A+ve blood but their children are born normally even when they have A+ve/B+ve blood(opposite of the mother). There even are people whose mothers have O+ve blood while they have B+ve/A+ve blood groups. The body haspre-madeaandbantibodies which should kill the fetus unlike in case of Rh where 1st birth is safe. Also much lesser time is needed to produce these antibodies which is why there cannot be any blood transfusion between incompatible ABO system blood types while one transfusion is possible between incompatible Rh blood types My take on this will be that antibodies against ABO blood groups can never cross placenta but most antibodies do so this seems less like a solution A lot of research failed me a solution. I found a somewhat similar question here but it does not address my query completely Erythroblastosis Foetalis

Answer 1

Antibodies to the Rh antigen are produced only in Rh individuals after exposure to the antigen. During or immediately after birth, a Rh¯ mother can be exposed to the baby's Rh cells. The mother's immune system begins to generate anti-Rh antibodies, which can cross the placenta into the fetal bloodstream and destroy the fetal RBCs.

Step-by-step explanation:

In contrast to the ABO group antibodies, which are preformed, antibodies to the Rh antigen are produced only in Rh individuals after exposure to the antigen. This process, called sensitization, occurs following a transfusion with Rh-incompatible blood or, more commonly, with the birth of an Rh* baby to an Rh¯ mother. Problems are rare in a first pregnancy, since the baby's Rh* cells rarely cross the placenta. However, during or immediately after birth, the Rh¯ mother can be exposed to the baby's Rh cells. Research has shown that this occurs in about 13-14 percent of such pregnancies. After exposure, the mother's immune system begins to generate anti-Rh antibodies. If the mother should then conceive another Rh* baby, the Rh antibodies she has produced can cross the placenta into the fetal bloodstream and destroy the fetal RBCs. This condition, known as hemolytic disease of the newborn (HDN) or erythroblastosis fetalis, may cause anemia in mild cases, but the agglutination and hemolysis can be so severe that without treatment the fetus may die in the womb or shortly after birth.