Chapter 17: Anemia of Prematurity

I. Intensive and convalescent care

1. Definition

   1. Anemia that develops in the neonatal period in term infants is typically defined by central venous hemoglobin of less than 13 g/dL or capillary hemoglobin of <14.5 g/dL.

   2. In healthy term infants, the nadir hemoglobin value rarely falls below 10 g/dL at an age of 10 to 12 weeks. Because this postnatal drop in hemoglobin level in term infants is well tolerated and requires no therapy, it is commonly referred to as the physiological anemia of infancy.

   3. In contrast, this decline is more rapid (ie, nadir at 4 to 6 weeks of age) and the blood hemoglobin concentration falls to lower levels in infants born prematurely—to approximately 8 g/dL in infants with birthweights of 1.0 to 1.5 kg and approximately 7 g/dL in infants with birthweights <1 kg.

   4. Consequently, because the pronounced decline in hemoglobin concentration that occurs in many ELBW infants is associated with abnormal clinical signs and need for allogeneic RBC transfusions, the anemia of prematurity is not accepted to be a physiological and benign event.

   5. Physiologic and nonphysiologic factors related to prematurity are responsible for the anemia of prematurity, though there are no specific hemoglobin values defining the condition in preterm populations.

2. Incidence

   1. All healthy, term newborn infants have a high blood hemoglobin level (15 to 20 g/dL) at birth due to relative hypoxia in utero.

   2. Some extremely preterm neonates will have slightly lower values than term infants (eg, 13 g/dL), and occasional neonates will have higher values (eg, 22 g/dL).

   3. Regardless of the level at birth, all experience a fall in hemoglobin levels over the first weeks of life, with term infants reaching a nadir level of about 11.5 g/dL at 12 weeks of life. In contrast, preterm infants experience a more profound and rapid drop in hemoglobin levels, which may result in severe anemia requiring red blood cell (RBC) transfusions.

   4. Approximately 90% of ELBW neonates will receive at least one RBC transfusion, typically during the first weeks of life.

   5. Because of efforts to minimize the amounts of blood drawn from neonates for laboratory testing and to transfuse more conservatively (ie, to accept lower pretransfusion hematocrit [HCT] values), the number of RBC transfusions given to preterm infants has dropped over the years.

3. Pathophysiology

   Several physiological factors play a role in the pathogenesis of the anemia of prematurity.

   1. All neonates experience a decline in circulating RBCs during the first weeks of life. This decline results both from multiple physiological factors and, in sick preterm infants, from several additional factors—the major one being phlebotomy blood losses for laboratory testing.

   2. Because ELBW infants are born before the third trimester of gestation, they are deprived of most of the iron transported from the mother and miss out on a great deal of in utero fetal erythropoiesis.

   3. Extrauterine body growth is extremely rapid during the first months of life, and RBC production by neonatal marrow must increase commensurately.

   4. It is widely accepted that the circulating life ...