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Early Clamping Denies Baby Blood Supply for Pulmonary Perfusion

Very early clamping results in less than physiologic blood volume. The normal, term child routinely survives, but clamping the cord of a compromised child before ventilation is riskier. Initial aeration of the lungs causes reflex dilatation of pulmonary arterioles and a massive increase in pulmonary blood flow. Placental transfusion normally supplies this volume. Clamping the cord before the infant's first breath results in blood being sacrificed from other organs to establish pulmonary perfusion. Fatality may result if the child is already hypovolemic.

Because placental transfusion patterns vary widely, it is futile to attempt to give the newborn the "right" amount of blood by clamping at a set time after birth. However, it is extremely likely that the infant will have less-than-optimal blood volume if the cord is clamped before the lungs are ventilated.

In clinical practice, late clamping produces a high hematocrit, high blood pressure, and vasodilatation to accommodate the large volume of blood. These latter two factors should increase tissue perfusion. In searching the literature, I was unable to find any documented case of hyperviscosity syndrome in which the cord was clamped late, although I did find many documented cases of late clamping involving normal newborns with high hematocrits.

There are, however, many documented cases of hyperviscosity syndrome with high hematocrits (e.g., cases involving gestational diabetes or postmaturity) in which the cord was clamped before physiologic cord closure, thus creating low blood volume, low blood pressure, and vasoconstriction coupled with the polycythemia. The inadequate tissue perfusion is blamed on the high hematocrit, when the root cause of the hyperviscosity syndrome is hypovolemic vasoconstriction enforced to the fourth power.

-excerpted from George M. Morley, MB., CH. B, Cord Closure: Can Hasty Clamping Injure the Newborn? July 1998 OBG Management.