Page 27, Developmental Pathophysiology, Develop. Physiol., Dr. D. Penney



Blood Volume at Birth:

In a full-term fetus the placenta contains 125 ml of blood, 33% of the total blood volume. During the first 30 sec. post-delivery 75 ml/kg of blood is transferred to the newborn (Table 4.27). If fetal blood volume was adequate in utero, why shouldn't it be adequate after birth? Should placental blood be added to the fetus to fill the expanding lungs? Maybe the extra blood could be used to correct fetal anemia; however, anemia is rare in newborns and the extra volume could overload the CV system.

After adding extra placental blood, plasma volume decreases rapidly, and as a consequence, hematocrit is elevated. The extra volume results in increased urine flow, capillary engorgement, transudation of plasma, tachycardia, tachypnea, increased stroke volume, hyperbilirubinemia, lower lung compliance, and in some infants, the hyperviscosity syndrome. The flow chart in Figure 4.11 shows the course of events in both intrauterine hypoxia and in placental transfusion.


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