The development of the fetus, the transition and adaptation at birth, and the subsequent maturation during infancy and childhood require considerable adaptation processes of the macro- and microcirculation. The fetus lives in a severely hypoxic atmosphere with an oxygen saturation of 65 to 70% in blood flowing to vital organs such as the brain. This borderline oxygen supply makes the fetus extremely vulnerable to hypoxicischemic events. At birth, the cardiovascular system undergoes eminent changes such as the sudden interruption of placental blood flow and the redistribution of cardiac output to the pulmonary arteries. Moreover, the neonate is at high risk to acquire disorders with strong impact on blood circulation (e.g., septicemia). The circulation continues to show marked changes with growth and further organ differentiation during infancy and childhood.

Peculiar rheologic properties of blood appear to play an important role in the maintenance of high blood flow conditions in spite of very low blood pressure in the fetus and neonate [1]. On the other hand, sudden changes of rheologic properties may develop in the perinatal period with marked effects on circulation such as polycythemia resulting from placental transfusion [2].

This overview is designed to describe the physiology and pathophysiology of hemorheological parameters during the fetal and neonatal period. In addition, some information on developmental hemorheology during infancy and childhood will also be presented.