Neonatal coagulation: normal physiology and pathophysiology.

The newborn infant, particularly when premature, has a haemostatic mechanism which may not be entirely capable of withstanding the onslaughts of trauma, infection, asphyxia or other complications of the neonatal period. He is at risk of local or diffuse haemorrhage, which may at times be serious or even life-threatening. The cause of haemorrhage during the newborn period can generally be ascertained by a careful history and brief physical examination directed toward recognition of any predisposing factors or underlying diseases. Screening laboratory tests can usually be correctly interpreted as long as certain laboratory artifacts and physiological peculiarities of the neonatal coagulation mechanism are kept in mind. Diagnosis of and therapy for vitamin K deficiency and haemophilia in the healthy-appearing neonate is generally carried out with little difficulty. The seriously ill neonate with bacterial sepsis, respiratory distress syndrome, or extreme immaturity presents greater problems, for laboratory tests may be more difficult to obtain and interpret and underlying conditions may be untreatable. DIC occurs commonly in such neonates, and transfusion therapy, with or without heparin, is often unsuccessful. A persistent dilemma are those neonates with fatal intravascular haemorrhage, in whom definable haemostatic abnormalities are few and transfusion therapy is futile.