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When should the Anti-D injection be administered during pregnancy?

Q: My wife has AB (RH -ve) blood group. She is pregnant and running the 9th month. My blood group is A+. Our first baby is normal and her blood group is A+. After the first delivery, my wife got an injection called Anti-D, for negative Rh in the mother as the baby and the father were positive. The second pregnancy will be delivered by next week, but till date she hasn't taken any Anti-D injection. The doctor told me that if the time has already passed then you have to wait till delivery to take the injection. When should the Anti-D injection be injected? Is it during pregnancy of after delivery? Which month is suitable for injection?

A:The Rh (rhesus) factor is a protein (antigen) present on the surface of red blood cells (RBCs). 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 antibodies against this protein (called Rh antibodies). 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. The diagnostic evaluation includes maternal prenatal ABO and Rh typing, and an antibody screen. Depending on the results of the antibody screen, maternal antibody titers, and paternal and/or fetal RBC phenotyping are performed. If fetal RBC express the antigen against which maternal alloimmunization has occurred, the pregnancy is then followed by measuring serial maternal antibody titers and abdominal sonograms. Pregnant d mothers should have regular indirect antiglobulin tests. As a guide anti-D antibody levels < 0.2 mg/ml require no action while higher levels require action; levels > 2.0 mg/ml typically are associated with severe disease. Prevention of HDN is now carried out with anti-D Ig (intramuscular within 72 hours of delivery) in all d mothers giving birth to a D child. A Kleihauer test for foetal haemoglobin can be used as a guide for the dose of anti-D Ig to be administered.


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