Introduction

Polycythemia and hyperviscosity were first associated with adverse neurologic events and sequelae in a series of case reports. The first case often referenced was published by Wood in 1952 and was followed by a small series of infants with polycythemia and hyperviscosity who displayed multiple problems, including cerebral dysfunction. Since those early reports it has become clear that polycythemia has multiple etiologies which influence whether and which problems may be associated with it in the newborn period. In addition more recent animal and human studies have clarified the relationship between polycythemia and alterations in function of various organs.

Definition

Polycythemia is usually defined in the literature as a hematocrit value ≥ 65% when the blood sample is obtained from a free-flowing, large venous blood vessel such as the inferior vena cava (umbilical vein sample) spun in a centrifuge. Sampling from small vessels with low flow or capillary samples will have higher values. In addition, hematocrits calculated by a Coulter counter will yield comparatively lower values. Independent of sample site or measurement technique, the hematocrit increases over the first 2–4 h of life, gradually returning to the birth value by 12–24 h of age.

Incidence

The incidence of polycythemia varies by definition, altitude of the population, pregnancy risk factors, and techniques involved in the delivery of the fetus, and timing and sampling sites of blood samples.