Q: My blood group is B positive and my wife's is B negative. She is pregnant and is in the 9th month and just had a blood test for ICT and the doctor says that there is a risk in delivery as we both want a normal delivery. The doctor says that since the baby is B positive, she will have to operate. Is there no chance for a normal delivery?

A:There are about 20 known blood group systems that consist of over 200 antigens. Only two of these, however, (the ABO and the Rh) can commonly cause haemolytic transfusion reaction (HTR) as well as haemolytic disease of the newborn (HDN). A mother gets sensitised when the baby's red blood cells (RBCs) carrying inherited paternal RBC antigens which are not present on mothers RBC pass into the maternal circulation, inducing antibody formation. These antibodies can then cross the placenta and coat the babys RBC that in turn are removed by the body. In most pregnancies the transplacental haemorrhage is less than 0.1 mL, and thus women can get sensitised as a result of small undetectable fetomaternal haemorrhage. Sensitisation can also occur as a result of a previous miscarriage, amniocentesis and blood transfusion and is more likely if mother and foetus are ABO compatible. In a subsequent pregnancy entry of even a few fetal red blood cells into the maternal circulation induces a secondary anti-D response and such antibodies can cross the placenta and bind red blood cells. The clinical features of HDN depend on the titre (levels) and affinity of maternal anti-D antibodies. In severe cases intrauterine death occurs from hydrops fetalis; in milder cases the foetus is born live with severe anaemia, jaundice, oedema and hepatosplenomegaly. Diagnosis is by the presence of erythroblasts, high reticulocyte count and a positive direct antiglobulin test (DAT) in cord blood and a positive indirect antiglobulin test (IAT) in maternal blood. 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 alloimmunisation 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 (intramusccular 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.