Umbilical cord acid base changes associated with perinatal cardiac failure.

Two infants delivered by emergency cesarean section because of fetal distress are described, and the umbilical blood acid-base findings are discussed. One fetus was stillborn, the other died in the immediate neonatal period, and both showed signs of cardiac dilation and failure on postmortem examination. Umbilical cord blood gas determination at the time of delivery showed almost normal values of pH, PcO2, and PO2 in the umbilical vein but acidotic pH with high PCO2 and low PO2 values in the umbilical artery samples. These findings are probably the result of a prolonged umbilical blood circulation time because of fetal cardiac failure. This sluggish perfusion allows the equilibration of fetal blood with maternal intervillous blood, and the findings in the fetal umbilical vein approximate maternal uterine venous values. Umbilical cord acid-base determinations in perinatal surveillance are commonly recommended without specific details. Umbilical artery samples must be obtained to properly assess the metabolic status of the fetus at the time of birth.