Why have I not conceived in spite of receiving the anti-D injection?

Q: I am 32 years old. I became Rh negative sensitised after my first pregnancy eight years back. My blood group is AB -ve and my husband’s is A +ve. My first baby is AB +ve. I had taken the anti-D injection after my delivery. After this I conceived 4 times, but during each pregnancy I encountered problems of antibodies infection, which resulted in termination of the pregnancies. Please advise on this matter.

A: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.The diagnostic evaluation includes maternal prenatal ABO and Rh typing, and an antibody screen. Depending on the results of the antibody screen, maternal antibody titres, and paternal and/or fetal RBC phenotyping are performed. If fetal RBCs express the antigen against which maternal alloimmunisation has occurred; the pregnancy is then followed by measuring serial maternal antibody titres 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 Haemolytic disease of newborns (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 fetal haemoglobin can be used as a guide for the dose of anti-D Ig to be administered.