Sequential changes in placental blood gases and pH during the hour following delivery.

We studied the effect of a delay in blood sampling on the measurement of placental blood gases, pH and calculated bicarbonate. Blood was sampled serially at 15-minute intervals during the hour following delivery from placentas and attached umbilical cords of unasphyxiated term neonates. Placentas and attached cords were stored at room temperature. When blood was sampled exclusively from the segment of the umbilical vein lying within the umbilical cord, there were no statistically significant changes during the time of study in pH, PCO2 or PoO2. When some or all of the serial samples were taken from vessels on the surface of the placenta, there was a statistically and biologically significant decrease in the pH and increase in the PCO2 values of the blood. Our results indicate that the validity of the measurements of umbilical venous blood gases and pH is not affected by up to an hour's delay in blood sampling.