Q: My blood group is B- and my wife is B+. Will there be any complications during pregnancy? If there is any, what precautions should we take?

A:The red blood cells (RBCs) present in our body have proteins on them called antigens, which play a role in blood transfusion and tissue typing. Each group of antigens (and their antibodies) comprises a blood group system and about 20 Blood group systems are known till date. The most important are the ABO and Rh systems, the mismatch of which can lead to major transfusion reactions. In the Rh system either we have the Rh antigen (Rh positive) or lack it (Rh negative). There are no naturally occurring Rh antibodies in our blood and an Rh negative individual forms them if exposed to Rh positive red cells. Rh incompatibility (or Rh disease) is a state in which a woman with Rh-negative blood group is exposed to Rh-positive RBCs leading to the formation of Rh antibodies against this protein. Once these antibodies are made in the mother, they cross the placenta into the developing baby’s circulation and destroy the baby’s RBCs, which are Rh +. This can occur when an Rh-negative woman is carrying an Rh-positive baby or if an Rh-negative woman receives blood transfusion containing Rh-positive cells. In either case, her immune system is exposed to the Rh antigen (which is ‘foreign’ to her body) and begins producing Rh antibodies. During pregnancy and delivery, red cells from the baby enter the mother’s circulation. If the exposure is significant, the mother gets sensitised and begins to produce antibodies. When these antibodies cross the placenta and enter the baby’s circulation, they encounter Rh + cells, which are then destroyed by these antibodies leading to anaemia and jaundice in the baby. Delivery is the usual time when sensitisation occurs and thus, first-born babies are usually unaffected, as antibodies have not yet formed in the mother. A subsequent pregnancy with an Rh-positive baby can give rise to anaemia in the baby as these antibodies destroy the baby’s RBCs. Each successive pregnancy poses a greater risk to the baby. It is postulated that even less than 1 ml of Rh-positive blood can induce antibody formation while several studies have shown that ~30% Rh-negative individuals never form antibodies despite exposure to Rh antigen. But if the mother's immune system is kept from seeing the fetal red cells, she will never make antibodies to the Rh antigens. This can be accomplished by giving the new mother an injection of antibodies directed against the Rh antigens on the fetal RBC. The current recommendation is that every Rh-negative non-immunized woman who presents with ante-partum bleeding or potential feto-maternal haemorrhage should receive 300 mcg of Rh IgG injection. For every 30 mL of fetal whole blood exposed to maternal circulation, 300 mcg of Rh IgG should be administered. You need not worry as blood grouping is done as a part of the antenatal check-up followed by an ultrasound examination and standard protocols exist for handling Rh negative pregnant women.