Hemolytic disease of the newborn, also known as
hemolytic disease of the fetus and newborn,
HDN,
HDFN, or
erythroblastosis fetalis, is an
alloimmune condition that develops in a
fetus, when the
IgG molecules (one of the five main types of
antibodies) produced by the mother pass through the
placenta. Among these antibodies are some which attack the
red blood cells in the fetus' circulation, which are broken down and destroyed (
hemolysis). The fetus can develop
reticulocytosis and
anemia. 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 (immature red blood cells) are present in the fetal blood, and so these forms of the disease can be called
erythroblastosis fetalis (or
erythroblastosis foetalis).