Blood and Anemia of Prematurity

The hematopoetic system

The hematopoetic system is responsible for producing all the components that make up blood. The system works by first producing stem cells that multiply and develop into more specialized blood cells: red cells to carry oxygen; white cells to fight infection; and the platelets needed for blood clotting. A fetus produces blood in the bone marrow but, unlike adults, also in other parts of the body such as the liver. Additionally, a fetus’s hemoglobin, a component of red blood cells, differs from the hemoglobin of an adult. A newborn baby’s hemoglobin production changes from fetal hemoglobin (Hgb F) to adult hemoglobin (Hgb A). This is significant because some blood problems cannot be diagnosed until the transition from producing Hgb F to Hgb A has been completed, which is usually after the first 2 months of life.

Blood problems, of which there are many, may be genetic in origin and may interfere with the production of one or more of the components that make up the blood.


In adults and babies alike, new red blood cells are constantly being produced and old ones broken down in the body. This process tends to occur in cycles, so there can be more or less red blood cells than average in the body at any given time. For premature babies, this cycle of red cell break down is usually more pronounced and red cell production may be slower.

The production of red blood cells is initiated by a hormone called erythropoietin or EPO. When a baby is born, the production of EPO tends to drop off slightly and there is a corresponding drop in the production of red blood cells. Additionally, premature babies have blood taken frequently for tests to monitor their medical condition and to help guide their treatment. The sum of these factors results in anemia, a deficiency of red blood cells. Although mild anemia is not particularly dangerous, severe anemia can be serious, as red blood cells are responsible for the transport of oxygen throughout the body. Severe anemia can adversely affect overall strength and growth, which can complicate other conditions.

The usual treatment of severe anemia is with blood transfusions to replace the depleted red blood cells. Premature babies commonly require blood transfusions for anemia.  In special circumstances, babies may be given EPO to stimulate the production of red blood cells. Usually administered by injection three times a week, EPO will be given until the baby has reached the equivalent of about 36 weeks’ gestation, at which time natural production of EPO should be sufficient to produce enough red blood cells.

A baby with anemia may also require iron supplements, since iron is essential for red blood cell production. Iron supplements taken by mouth are started when the baby is mature enough to tolerate milk feeds. After iron supplementation, the desired increase in red blood cell production will take several weeks.

More information

Andrew James, BSc, MBChB, FRACP, FRCPC

Aideen Moore, MD, FRCPC, MRCPI, MHSc