Umbilical arterial-venous blood gas difference: a novel expression of placental respiratory function.

We applied the concept of umbilical arterial and venous (A-V) blood gas difference in evaluating placental respiratory function to establish normative values for these relationships. Umbilical A-V cord blood gas samples were obtained in standardized fashion in uncomplicated singleton pregnancies. A-V pO (2) and A-V pCO (2) differences were related to obstetric factors, placental weight, and gestational age. Mean absolute differences in uncomplicated vaginal deliveries between umbilical artery and umbilical vein were: pO (2) 11.4 +/- 7.0 mm Hg and pCO (2) 11.9 +/- 6.8 mm Hg. Values in nonlabor cesarean section cases did not differ significantly from those of cases delivered vaginally. A-V pO (2) differences did not vary significantly across gestation (Pearson's R = 0.05, P = 0.43) and did not correlate with birth weight ( R = 0.06, P = 0.30). A-V pCO (2) differences showed increases with gestational age ( R = 0.15, P = 0.008) and with birth weight ( R = 0.18, P = 0.002). Results similar to those of women delivered vaginally were seen in nonlabor cesarean deliveries. Duration of labor did not impact the A-V blood gas relationship. Umbilical A-V oxygen differences reflect placental respiratory function independent of gestational age, birth weight, duration of labor, and mode of delivery. They are easy to collect and represent a potentially valuable resource for assessment of placental function.