Hemolytic disease of the newborn

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Haemolytic disease of the newborn is an alloimmune condition that develops in a fetus, when the IgG antibodies that have been produced by the mother and have passed through the placenta include ones which attack the red blood cells in the fetal circulation. The red cells are broken down and the fetus can develop reticulocytosis and anaemia. This fetal disease ranges from mild to very severe, and fetal death from heart failure (hydrops fetalis) can occur. When the disease is moderate or severe, many erythroblasts are present in the foetal blood and so these forms of the disease can be called erythroblastosis fetalis (or erythroblastosis foetalis).

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Antibodies are produced when the body is exposed to an antigen foreign to the make-up of the body. If a mother is exposed to an alien antigen and produces IgG (as opposed to IgM which does not cross the placenta), the IgG will target the antigen, if present in the fetus, and may affect it in utero and persist after delivery. The three most common models in which a woman becomes sensitized toward (i.e., produces IgG antibodies against) a particular blood type are:

• Fetal-maternal hemorrhage can occur due to trauma, abortion, childbirth, ruptures in the placenta during pregnancy, or medical procedures carried out during pregnancy that breach the uterine wall. In subsequent pregnancies, if there is a similar incompatibility in the fetus, these antibodies are then able to cross the placenta into the fetal bloodstream to attach to the red blood cells and cause hemolysis. In other words, if a mother has anti-RhD (D being the major Rhesus antigen) IgG antibodies as a result of previously carrying a RhD-positive fetus, this antibody will only affect a fetus with RhD-positive blood.

• The woman may receive a therapeutic blood transfusion with an incompatible blood type. ABO blood group system and Rhesus blood group system typing are routine prior to transfusion. Suggestions have been made that women of child bearing age or young girls should not be given a transfusion with Rhc-positive blood or Kell₁-positive blood to avoid possible sensitization, but this would strain the resources of blood transfusion services, and it is currently considered uneconomical to screen for these blood groups.

• The third sensitization model can occur in women of blood type O. The immune response to A and B antigens, that are widespread in the environment, usually leads to the production of IgM anti-A and IgM anti-B antibodies early in life. On rare occasions, IgG antibodies are produced. In contrast, Rhesus antibodies are generally not produced from exposure to environmental antigens.

• Acquired hemolytic anemia
• Congenital toxoplasma
• Syphilis infection
• Congenital obstruction of the bile duct and cytomegalovirus infection.

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Complications of HDN could include

• Kernicterus
• Hepatosplenomegaly
• Inspisated (thickened or dried) bile syndrome and/or greenish staining of the teeth
• Hemolytic anemia and damage to the liver due to excess bilirubin.

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