Anemia
Anemia is a disorder in which there are too few red blood cells in the blood.
Normally, the newborn's bone marrow does not produce new red blood cells between birth and 3 or 4 weeks of age. Anemia can occur when red blood cells are broken down too rapidly, too much blood is lost, or more than one of these processes occurs at the same time.
Any process that leads to red blood cell destruction, if sufficiently severe, results in anemia and high levels of bilirubin (hyperbilirubinemia). Hemolytic disease of the newborn may cause the newborn's red blood cells to be destroyed rapidly. The red blood cells may also be rapidly destroyed if the newborn has a hereditary abnormality of the red blood cells. An example is hereditary spherocytosis, in which the red blood cells appear small and spherical in shape when viewed under a microscope.
Infections acquired before birth, such as toxoplasmosis, rubella, cytomegalovirus, herpes simplex, or syphilis, may also rapidly destroy red blood cells, as can bacterial infections of the newborn acquired during or following birth.
Another cause of anemia is blood loss. Blood loss can occur in many ways, for example, if there is a large transfusion of the fetal blood across the placenta and into the mother's circulation (fetal-maternal transfusion) or if too much blood gets trapped in the placenta at delivery, when the umbilical cord is clamped. The placenta may separate from the uterine wall before delivery (placental abruption), leading to hemorrhage of the fetal blood. Rarely, anemia may result from a failure of the fetal bone marrow to produce red blood cells. One example of this is a genetic disorder called Fanconi's anemia. Another rare example is that due to exposure of the mother and fetus to certain drugs used during pregnancy.
Symptoms and Treatment
A newborn who has suddenly lost a large amount of blood during labor or delivery may appear pale and have a rapid heart rate and low blood pressure, along with rapid, shallow breathing. Milder anemia may result in lethargy, poor feeding, or no symptoms. When the anemia is a result of rapid breakdown of red blood cells, there is also increased production of bilirubin, and the newborn's skin and the whites of the eyes appear yellow (jaundice).
A newborn who has rapidly lost a large amount of blood, often during labor and delivery, is treated with intravenous fluids followed by a blood transfusion. Very severe anemia caused by hemolytic disease may also require a blood transfusion, but the anemia is more often treated with an exchange blood transfusion, in which part of the newborn's blood is gradually removed and replaced with equal volumes of fresh donor blood. The exchange transfusion also removes bilirubin in the circulation and thus treats the hyperbilirubinemia.
 See the sidebar What Is Hemolytic Disease of the Newborn?
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