Ex-vivo evidence of the human umbilical cord as a physiological buffer against fetal acidosis

The human umbilical cord at term typically consists of two arteries and one vein. Fetuses with a single umbilical artery are known to have increased risk of perinatal morbidity and mortality. However, the role of the dual umbilical artery in reducing these risk remains poorly understood. In this work, we hypothesize that the increased arterial wall surface provided by the dual umbilical artery facilitates the diffusion of carbon dioxide (CO₂) between the fetal blood and Wharton's jelly to allow temporary CO₂ storage.

We flushed blood plasma with high and low CO₂ content through umbilical cord segments, and measured the blood gas content of the outflowing liquid periodically.

The hypothesized diffusion was proven by a linear relationship between estimated diffusion capacity and cord length for three different experimental analyses (all p < 0.001).

This diffusion capacity provides a threefold protection of the fetus from acidosis during uterine contractions. Firstly, the cord dampens the increase in CO₂ in the fetal blood during a contraction, thereby protecting against acute acidosis. Secondly, the diffusion of CO₂ from Wharton's jelly back into the arterial blood accelerates fetal recovery after a contraction through its interaction with the Bohr and Haldane effects. Finally, our results indicate a diffusion capacity for oxygen as well, through which the umbilical cord may act as a fetal oxygen reserve. Since the study design does not allow for estimation of the clinical relevance of this threefold effect, future research should focus on determining the clinical impact of this diffusion capacity, enabling the adaptation of obstetric management strategies for fetuses with relevant cord anomalies.