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Hematologic problems arise frequently in the newborn period.1 This section is focused on disorders specific to the newborn period. For further discussion of the developmental changes that occur in hematopoiesis, see Chapter 429. Hematologic disorders, including congenital disorders, are discussed in detail in Section 23: Disorders of the Blood.

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Nucleated Red Blood Cells

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Nucleated red blood cells (nRBCs) are not common in older children but can be found frequently in the peripheral blood smear of newborns.8 They represent circulating erythrocyte precursors, or normoblasts, which are normally found in the bone marrow. Healthy term newborns may have some nRBCs in the peripheral blood. However, elevated nRBCs may represent the result of pathologic processes such as relative in utero hypoxia resulting in increased erythropoietin, which stimulates increased production of red blood cells. Although many laboratories report nRBCs in relation to the number of white blood cells (nRBCs/100 WBC), it is probably more informative to express this as an absolute number per unit volume (ie, nRBCs/mm3). A value of 1000 nRBCs/mm3 may be considered the higher limit of normal for a normal term newborn. Preterm newborns typically have higher nRBCs at birth.

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An increase in the number of circulating nRBCs can represent conditions of increased erythropoiesis or stress-mediated release of normoblasts from the bone marrow. Increased erythropoiesis may occur in times of chronic hypoxia as in preeclampsia and placental insufficiency. Infants born to smoking mothers have been found to have increased nRBCs.9 Increased erythropoiesis may result from blood loss from any cause, including hemolysis, which occurs in the context of red blood cell isoimmunization. Elevation of nRBCs also occurs in infants of diabetic mothers and in congenital infections.

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Hypoxia does not have to be chronic to observe nRBC elevation at birth. Acute stress and subacute stress are also associated with increased circulating nRBCs. Elevated nRBCs in this context may serve as a marker for fetal asphyxia.10,11 Increased numbers of nRBCs correlates with lower umbilical cord pH and therefore may reflect degree and duration of asphyxia.12,13 Chronic asphyxia is typically associated with higher nRBCs than with acute asphyxia events.14

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Anemia

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The mean hemoglobin concentration in the term newborn ranges from 14 to 20 g/100 mL.15 In the first hours after birth, the hemoglobin concentration can rise due to a relative reduction in plasma volume. However, the hemoglobin level soon begins to decline, reaching a “physiologic nadir” at around 2 to 3 months of age. Preterm newborns have lower hemoglobin concentrations at birth and a larger decrease after birth, reaching a nadir at an earlier age, as early as 6 weeks for very-low-birth-weight infants.16 The causes of anemia in the newborn period include increased blood loss or decreased production of red blood cells.

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Blood loss may occur before, during, or after birth. Fetal-to-maternal ...

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