Umbilical Arterial-Venous Blood Gas Difference: A Novel Expression of Placental Respiratory Function

ABSTRACT

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 pO₂ and A-V pCO₂ 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: pO₂ 11.4 ± 7.0 mm Hg and pCO₂ 11.9 ± 6.8 mm Hg. Values in nonlabor cesarean section cases did not differ significantly from those of cases delivered vaginally. A-V pO₂ 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 pCO₂ 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.

KEYWORDS

Arterial-venous blood gas difference - placenta - oxygenation - umbilical cord blood gas

REFERENCES

• 1 ACOG Committee on Obstetric Practice . ACOG Committee Opinion No. 348, November 2006: Umbilical cord blood gas and acid-base analysis.  Obstet Gynecol. 2006;  108 1319-1322
• 2 Goldaber K G, Gilstrap III L C, Leveno K J, Dax J S, McIntire D D. Pathologic fetal acidemia.  Obstet Gynecol. 1991;  78 1103-1107
• 3 Cunningham F G, Leveno K J, Bloom S L, Hauth J C, Gilstrap III L, Wenstrom K D. Umbilical cord blood acid-base studies. In: Williams Obstetrics. 22nd ed. New York; McGraw-Hill 2005: 639-640
• 4 Carter A M. Factors affecting gas transfer across the placenta and the oxygen supply to the fetus.  J Dev Physiol. 1989;  12 305-322
• 5 Gregg A R, Weiner C P. “Normal” umbilical arterial and venous acid-base and blood gas values.  Clin Obstet Gynecol. 1993;  36 24-32
• 6 Yeomans E R, Hauth J C, Gilstrap III L C, Strickland D M. Umbilical cord pH, pCO₂ and bicarbonate following uncomplicated term vaginal deliveries.  Am J Obstet Gynecol. 1985;  151 798-800
• 7 Richardson B, Nodwell A, Webster K, Alshimiri M, Gagon R, Natale R. Fetal oxygen saturation and fractional extraction at birth and the relationship to measures of acidosis.  Am J Obstet Gynecol. 1998;  178 572-579
• 8 Adrogue H J, Rasha M N, Gorin A B, Yacoub J, Madia N E. Assessing acid-base status in circulatory failure. Differences between arterial and central venous blood.  N Engl J Med. 1989;  320 1312-1316
• 9 Belai Y, Goodwin T M, Durand M, Greenspoon J S, Paul R H, Walther F J. Umbilical arteriovenous pO₂ and pCO₂ differences and neonatal morbidity in term infants with severe acidosis.  Am J Obstet Gynecol. 1998;  178 13-19
• 10 Longo L D. Respiration in the fetal-placental unit. In: Cowett RM Principles of Perinatal-Neonatal Metabolism. New York; Springer-Verlag 1991: 304
• 11 Cheng Y W, Hopkins L M, Laros R K, Caughey A B. Duration of the second stage of labor in multiparous women: maternal and neonatal outcomes.  Am J Obstet Gynecol. 2007;  196 585.e1-e6