Hemolytic disease of the newborn, also known as hemolytic disease of the fetus and newborn, HDN, HDFN, or erythroblastosis fetalis,[1][2] is an alloimmune condition that develops in a fetus at or around birth, when the IgG molecules (one of the five main types of antibodies) produced by the mother pass through the placenta.

After delivery, bilirubin is no longer cleared (via the placenta) from the neonate's blood and the symptoms of jaundice (yellowish skin and yellow discoloration of the whites of the eyes, or icterus) increase within 24 hours after birth.

Untreated profound anemia can cause high-output heart failure, with pallor, enlarged liver and/or spleen, generalized swelling, and respiratory distress.

[5] Complications of HDN could include kernicterus, hepatosplenomegaly, inspissated (thickened or dried) bile syndrome and/or greenish staining of the teeth, hemolytic anemia and damage to the liver due to excess bilirubin.

The maternal blood is likely to secrete more antibodies and attack the fetal erythrocytes during subsequent pregnancies because of re-exposure to the antigen.

[15] The three most common models in which a woman becomes sensitized toward (i.e., produces IgG antibodies against) a particular antigen are hemorrhage, blood transfusion, and ABO incompatibility.

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 their destruction (hemolysis).

HDFN can also be caused by antibodies to a variety of other blood group system antigens, but Kell and Rh are the most frequently encountered.

The immune response to A and B antigens, which are widespread in the environment, usually leads to the production of IgM or IgG anti-A and anti-B antibodies early in life.

[23][24][25] Anti-M also recommends antigen testing to rule out the presence of HDN as the direct coombs can come back negative in a severely affected infant.

It works by binding any fetal red blood cells with the D antigen before the mother is able to produce an immune response and form anti-D IgG.

Infants with Anti-M are also recommended to receive antigen testing to rule out the presence of HDN.

After birth, treatment depends on the severity of the condition, but could include temperature stabilization and monitoring, phototherapy, transfusion with compatible packed red blood, exchange transfusion, sodium bicarbonate for correction of acidosis and/or assisted ventilation.

[48] For this reason, she is advised to carry a medical alert card at all times and inform all doctors and emergency personnel of her antibody status.

Immune-mediated hemolytic reactions caused by IgG, Rh, Kell, Duffy, or other non-ABO antibodies typically result in extravascular sequestration, shortened survival of transfused red cells, and relatively mild clinical reactions.

Acute hemolytic transfusion reactions due to immune hemolysis may occur in patients who have no antibodies detectable by routine laboratory procedures.