Influence of arteries, vein and placenta interactions on the blood flow in the human umbilical cord.

The mechanisms governing umbilical venous return in early pregnancy remain incompletely understood, particularly the roles and interactions of arterial pulsatility, umbilical cord mechanics, and placental compliance. In this study, we combine numerical modelling and in vivo measurements to investigate hemodynamic and mechanical interactions within the feto-placental circulation. A fully coupled three-dimensional fluid-structure interaction model of the umbilical cord-comprising two pulsatile arteries, a compliant vein, and Wharton's jelly-was developed and connected to a zero-dimensional compliant placental model. The model incorporates arterial pressure pulsations, vessel wall deformation, and mechanical coupling within the closed arteries-placenta-vein system. In parallel, Doppler ultrasound measurements were performed in singleton pregnancies to assess umbilical venous flow at the placental insertion and in a free loop of the cord. Numerical results show that venous flow is dynamically modulated by arterial pulsations transmitted through both the cord and placenta, producing phase-shifted venous deformation and low-amplitude oscillations. Despite strong placental damping, the model predicts measurable venous flow oscillations with increasing amplitude toward the fetus. This behaviour depends on cord elasticity and placental compliance. The numerical model also points out that mechanical interactions between arteries, vein, and Wharton's jelly contribute positively to the mean flow rate, demonstrating a pulsometer-like effect. Doppler measurements confirm that venous flow is not strictly steady and that oscillation amplitude increases toward the fetus, which is consistent with simulations. Overall, our combined computational and in vivo approach reveals that the interplay between arterial pulsations and placental compliance is a key driver of umbilical venous return. Finally, beyond their physiological significance, our findings may contribute to the design and optimization of future artificial placenta and extracorporeal fetal support systems.