Hemolytic disease of the newborn (ABO) 4509624 201351734 2008-03-27T16:26:17Z Betacommand 509520 refs {{DiseaseDisorder infobox | Name = ABO HDN| ICD10 = {{ICD10|P|55|1|p|50}} | ICD9 = {{ICD9|773.1}} | }} 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 race|Caucasian]] populations about one fifth of all pregnancies have ABO incompatibility between the fetus and the mother, but only a tiny minority develop symptomatic ABO HDN<ref>http://www.obgyn.net/english/pubs/features/presentations/panda13/ABO-Rh.ppt</ref>. The latter only occurs in mothers of blood group O because they can produce enough IgG antibodies to cause hemolysis. == 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 ([[ABO blood group system|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 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. == Moderating factors == In about a third of all ABO incompatible pregnancies maternal IgG anti-A or IgG anti-B antibodies pass through the placenta to the fetal circulation leading to a weakly positive [[Coombs test#direct Coombs|direct Coombs test]] for the neonate's blood. However, ABO HDN is generally mild and short-lived and only occasionally severe because: * IgG anti-A (or IgG anti-B) antibodies that enter the fetal circulation from the mother find A (or B) antigens on many different fetal cell types, leaving fewer antibodies available for binding onto fetal red blood cells. * Fetal [[red blood cell|RBC]] surface A and B [[antigens]] are not fully developed during gestation and so there are a smaller number of antigenic sites on fetal RBCs. == Diagnosis == Routine [[obstetrics|antenatal]] antibody screening blood tests ([[Coombs test#indirect Coombs test|indirect Coombs test]]) do not screen for ABO HDN. If IgG anti-A or IgG anti-B antibodies are found in the pregnant woman's blood, they are not reported with the test results, because they do not correlate well with ABO HDN. Diagnosis is usually made by investigation of a newborn baby who has developed [[jaundice]] during the first day of life. == Treatment == [[Neonatal jaundice]] caused by ABO HDN is usually successfully treated with phototherapy, unless the ABO HDN is uncommonly severe. Treatment of moderate or severe HDN caused by ABO antibodies is similar to that for [[Rh disease]]. == References == <references/> * Mollison PL, Engelfriet CP and Contreras M. Blood Transfusion in Clinical Medicine. 1997. 10th edition. Blackwell Science, Oxford, UK. [1] www.obgyn.net/english/pubs/features/presentations/panda13/ABO-Rh.ppt == See also == * [[Coombs test]] * [[Hemolytic anemia]] * [[Hematology]] {{HDN}} [[Category:Blood disorders]] [[Category:Hematology]] [[Category:Obstetrics]] [[Category:Pediatrics]] [[Category:Transfusion medicine]]