Hemodynamics analysis of fetal intra-abdominal umbilical vein varix using computational fluid dynamics with Doppler ultrasound

Fetal intra-abdominal umbilical vein varix (FIUVV) is a rare but potentially risky fetal umbilical cord (UC) vascular anomaly closely related to adverse pregnancy outcomes. Clinically, the diagnosis of FIUVV primarily relies on Doppler ultrasound. Unfortunately, it is challenging to provide detailed FIUVV hemodynamics, while current in silico computational fluid dynamics (CFD) can provide these details with necessary ultrasound data. Therefore, this study uses CFD to simulate blood flow in four different geometric FIUVV models based on clinical Doppler ultrasound data. The varix region exhibited marked velocity deceleration, with a reduction of approximately 16-48% compared to the normal umbilical vein (UV) model. In addition, a large low-velocity region forms near the UV wall, where the slow-moving blood flow generates recirculating flow under the influence of the reverse pressure gradient. The pressure within the varicose region remains nearly equal to that at its entrance, while a distinct pressure gradient emerges near the exit of the varicose segment. Within the venous dilatation region, wall shear stress (WSS) decreased to 6% of that in the normal UV model. The downstream end of the varix region, the contraction of vessel diameter and velocity recovery lead to a sharp increase in WSS, with peak WSS reaching three times the normal value in the elongated fusiform and bilobed fusiform umbilical vein varix models. These results predispose to endothelial dysfunction and thrombogenesis and subsequently may impair fetal growth and development. These results underscore the critical role of CFD in elucidating FIUVV pathophysiology, particularly in quantifying thrombosis-prone low-shear zones and endothelial stress hotspots. The methodology provides novel insights into stratifying hemodynamic risks and optimizing prenatal monitoring protocols.