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Haemolytic Disease of Newborn (HDN)1. Haemolytic Disease of Newborn (HDN)Haemolytic disease of the newborn (HDN) is a condition in which the life span of the infant’s red cells is shortened by the action of antibodies derived from the mother by placental transfer. Antibodies in the mother are formed due to previous transfusion or by the entry of foetal red cells expressing paternally inherited antigens, into the maternal circulation. The most frequent antibody associated with HDN is anti-D.Natural History of Haemolytic Disease of Newborn (HDN) The haemotytic process due to maternal alloantibodies affecting the foetal red cells can vary greatly in severity. Mild In the mildest form there may be presence of an alloantibody in the mother with a positive DAT in the baby. However, no obvious signs of haemolysis are present. Moderate Moderate degree of severity is associated with anaemia and jaundice at birth. Haemolysis of sensitized (antibody coated) red cells occurs. The neonate may present with * anaemia * congestive cardiac failure * kernicterus Antibodies Associated with HDN The transfer of antibodies from the maternal to the foetal circulation takes place through the placenta. The only immunoglobulin transferred is IgG. Antibodies formed against Rh(D) antigen are the commonest cause of HDN. Classification of HDN According to the specificity of the antibody, haemolytic disease can be classfieid as 1. HDN due to.Rh(D) antibodies 2. HDN due to other Rh antibodies ie. anti-c, anti-E, anti-e. 3. HDN due to ABO IgG antibodies ABO - anti-A, anti-B 4. HDN due to other blood group system antibodies
Maternal anti-D, anti-K and anti-Fya antibodies are amongst the important causes of severe I-IDN. Anti-c is sometimes associated with severe I-IDN, while HDN associated with anti-E and anti-c is usually not severe. Rh haemolytlc disease (Rh-HDN) The D antigen is the most immunogenic of all blood group antigens and its corresponding antibody anti-D is capable of efficiently destroying red cells in vivo. Pathogenesis Rh immunization may occur due to pregnancy or transfusion of Rh positive blood. This can be explained as follows : 1.a) Rh Immunization of mother by foetal antigens Foetal red cells are known to cross the placenta and enter the maternal circulation. Transplacental haemorrhage (TPH) may occur during the last trimester of pregnancy, during labour or during obstetric manipulations. The likelihood of anti-D appearing in the maternal circulation depends on the size of TPH and the Rh phenotype of red cells. b) Rh Immunization by transfusion of Rh positivebibod When 200 ml or more of Rh (D) positive red cells are transfused to a Rh(D) negative subject, anti-D is detected within 2-5 months in almost 80% of recipients. This is a much m’ore powerful stimulus than transplacentral haemorrhage. 2. Placental transfer of antibo’dles from mother to foetus Transfer of antibodies occurs by their binding to Fc receptor bearing cells of the placenta. 3. Destruction of sensitized foetal red cells The sensitized RBCs attach to the macrophages by Fc fragment of IgO. This activates lytic and phagocytic processes leading to redcell destruction. Macrophages are the most important cellsinvolved in immune destruction. 4. Effect of ABO incompatibility ABO incompatibility in the mother and the foetus protects against Rh immunization, by causing destruction of ABO incompatible cells in maternal circulation
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