Chapter 93

### INTRODUCTION

The normal hematocrit of a healthy term infant ranges from 45% to 61%. This relatively high red cell mass is an adaptive response to the hypoxic intrauterine environment. Neonatal polycythemia, an abnormal elevation of red cell mass, is most often defined in textbooks as a venous hematocrit of 65% or more. It occurs in 1.5%–4% of healthy live births.1 Passive erythrocyte transfusion and increased fetal red cell production are 2 major causes for neonatal polycythemia.

Many patients are asymptomatic. When present, signs and symptoms are presumed to be secondary to associated hyperviscosity. Although not all polycythemic blood is hyperviscous, there is an exponential increase in blood viscosity when the hematocrit is 65% or higher, with a correlative decrease in oxygen transport (Figure 93-1). Poor oxygenation and microthrombi formation are believed to result in organ dysfunction in polycythemia. The central nervous, cardiopulmonary, endocrine, and gastrointestinal systems are commonly affected. Treatment of symptomatic polycythemia is partial exchange transfusion (XT). However, criteria for and benefit from this treatment are controversial.

###### FIGURE 93-1

Effect of hematocrit on blood flow, viscosity, and oxygen transport. (Adapted with permission from Glader.2)

### DIAGNOSIS AND INDICATION

#### Clinical Findings: History and Physical

Causes of polycythemia in neonates can be divided into 2 major categories: passive red blood cell (RBC) transfusion and increased erythropoiesis secondary to intrauterine hypoxia. During delivery, passive placental RBC transfusion can occur from delayed cord clamping or if the infant is held below the level of the introitus. Perinatal asphyxia and maternal oxytocin administration have also been known to increase placental RBC transfer to the fetus.3 In monochorionic twin pregnancies, twin-twin transfusion results in polycythemia in the recipient, who most commonly is the larger infant.

Increased erythropoiesis can occur in response to intrauterine hypoxia, and result in neonatal polycythemia. This is seen in pregnancies with placental insufficiency, which can result from multiple etiologies (Table 93-1). Increased erythropoiesis is also seen in pregnancies with increased fetal oxygen consumption, including congenital thyrotoxicosis and maternal diabetes.3

Table 93-1Factors and Conditions Associated With Neonatal Polycythemia

Polycythemia has been observed in neonates with trisomy 13, ...

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