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In ABO hemolytic disease of the newborn (also known as ABO HDN) maternal IgG antibodies with specificity for the ABO blood group system pass through the placenta to the fetal circulation where they can cause hemolysis of fetal red blood cells which can lead to fetal anemia and HDN. In contrast to Rh disease, about half of the cases of ABO HDN occur in a firstborn baby and ABO HDN does not become more severe after further pregnancies. The ABO blood group system is the best known surface antigen system, expressed on a wide variety of human cells. For Caucasian populations about one fifth of all pregnancies have ABO incompatibility between the fetus and the mother, but only a very small minority develop symptomatic ABO HDN.〔http://www.obgyn.net/english/pubs/features/presentations/panda13/ABO-Rh.ppt〕 The latter typically only occurs in mothers of blood group O, because they can produce enough IgG antibodies to cause hemolysis. Although very uncommon, cases of ABO HDN have been reported in infants born to mothers with blood groups A〔Wang, M, Hays T, Ambruso, DR, Silliman CC, Dickey WC. Hemolytic Disease of the Newborn Caused by a High Titer Anti-Group B IgG From a Group A Mother. Pediatric Blood & Cancer 2005;45(6): 861-862 〕〔Jeon H, Calhoun B, Pothiawala M, Herschel M, Baron BW. Significant ABO Hemolytic Disease of the Newborn in a Group B Infant with a Group A2 Mother. Immunohematology 2000; 16(3):105-8. 〕 and B.〔Haque KM, Rahman M. An Unusual Case of ABO-Haemolytic Disease of the Newborn. Bangladesh Medical Research Council Bulletin 2000; 26(2): 61-4.〕 ==Causes== * Environmental exposure Anti-A and anti-B antibodies are usually IgM and do not pass through the placenta, but some mothers "naturally" have IgG anti-A or IgG anti-B antibodies, which can pass through the placenta. Exposure to A-antigens and B-antigens, which are both widespread in nature, usually leads to the production of IgM anti-A and IgM anti-B antibodies but occasionally IgG antibodies are produced. * Fetal-maternal transfusion Some mothers may be sensitized by fetal-maternal transfusion of ABO incompatible red blood and produce immune IgG antibodies against the antigen they do not have and their baby does. For example, when a mother of genotype OO (blood group O) carries a fetus of genotype AO (blood group A) she may produce IgG anti-A antibodies. The father will either have blood group A, with genotype AA or AO, or more rarely, have blood group AB, with genotype AB. * Blood transfusion It would be very rare for ABO sensitization to be caused by therapeutic blood transfusion as a great deal of effort and checking is done to ensure that blood is ABO compatible between the recipient and the donor. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hemolytic disease of the newborn (ABO)」の詳細全文を読む スポンサード リンク
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