Perinatal Blood Loss
Richard A. Molteni MD1
1 Associate Professor of Pediatrics, University of Utah Medical Center, 50 North Medical Dr Salt Lake City, UT 84132
In recent years a great deal of attention has been paid to the evaluation and treatment of conditions characterized by red blood cell excess (polycythemia). The debatable practice of routine newborn hematocrit screening was initiated and perpetuated by the still uncertain short-term and long-term complications of polycythemia and its commonly associated state of hyperviscosity. Previously unsuspected anemia is often identified during this same screening process. Unless profound (leading to hypovolemic shock) or associated with more visible signs of hemolysis (jaundice), the etiology of this state of diminished red blood cell mass is often ignored or evaluated incompletely. This review focuses on the effects of anemia in the fetus and neonate, discusses mechanisms of fetal red blood cell production, and provides a basic diagnostic approach for the clinician when anemia is recognized in the neonatal period.
PHYSIOLOGIC EFFECTS OF RED CELL REDUCTION
Tissue Oxygen Delivery
Maintenance of adequate red blood cell numbers can be even more critical during fetal life than during the postnatal period. The fetus, dependent upon maternal oxygen sources, cannot raise tissue oxygen delivery acutely by increasing placental oxygen transfer, even when its red blood cell numbers are decreased. Total oxygen content (sum of oxygen dissolved in plasma and bound to hemoglobin) of the blood is dependent upon both the partial pressure of oxygen (Pao2) and the quantity of hemoglobin available.
