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 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 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.