Anemia of Prematurity - Portal Neonatal

Although EPO is not the only erythropoietic growth factor in the fetus, it is the most important. EPO is
synthesized in response to both anemia and hypoxia. The degree of anemia and hypoxia required to
stimulate EPO production is far higher for the fetal liver than for the fetal kidney. As a result, new
RBC production in the extremely premature infant (whose liver remains the major site of EPO
production) is blunted despite what may be marked anemia.
In addition, EPO, whether endogenously produced or exogenously administered, has a larger
volume of distribution and is eliminated more rapidly by neonates, resulting in a curtailed time for
bone marrow stimulation. Erythroid progenitors of premature infants are quite responsive to EPO
when that growth factor finally is produced or administered.
Shortened red blood cell life span or hemolysis
Secondly, the average life span of a neonatal RBC is only one half to two thirds that of the RBC life
span in an adult. Cells of the most immature infants may survive only 35-50 days. The shortened
RBC life span of the neonate is a result of multiple factors, including diminished levels of intracellular
ATP, carnitine, and enzyme activity; increased susceptibility to lipid peroxidation; and increased
susceptibility of the cell membrane to fragmentation.
Blood loss
Finally, blood loss may contribute to the development of AOP. If the neonate is held above the
placenta for a time after delivery, a fetal-placental transfusion may occur. More commonly, because
of the need to closely monitor the tiny infant, frequent samples of blood are removed for various
tests. Because the smallest patients may be born with as little as 40 mL of blood in their circulation,
withdrawing a significant percentage of an infant's blood volume in a short period is relatively easy.
In one study, mean blood loss in the first week of life was nearly 40 mL.
Taken together, the premature infant is at risk for the development of AOP because of limited
synthesis, diminished RBC life span, and increased loss of RBCs.
Frequency: In the US: Frequency of AOP is related inversely to the gestational age and/or
birthweight of the population. As many as 80% of infants with very low birthweight (VLBW) and 95%
of infants with extremely low birthweight (ELBW) receive blood transfusions during their
hospitalizations.
Mortality/Morbidity: Although a premature infant is unlikely to be allowed to become so anemic as
to die, complications from necessary blood transfusions ultimately can be responsible for the death
of a patient. Anemia is blamed for a variety of signs and symptoms, including apnea, poor feeding,
and inadequate weight gain.
Race: Race has no influence on the incidence of AOP.
Sex: Although the presence of testosterone in the male infant is believed to be at least partially
responsible for a slightly higher hemoglobin level at birth, this effect is of no significance with regard
to individuals with AOP.
Age:
• The more immature the infant, the more likely the development of AOP. AOP typically is not
a significant issue for infants born beyond 32 weeks' gestation.
• The nadir of the hemoglobin level typically is observed when the tiniest infants are aged 4-8
weeks.
• AOP spontaneously resolves by the time most patients are aged 3-6 months.