[Doppler ultrasound findings in umbilical cord abnormalities. An in vivo model for clarifying resistance relations of the fetoplacental circulation].

In cases with different umbilical cord anomalies the influence of foetoplacental resistance on the flow velocity wave forms is discussed. If there is no anastomosis between the two umbilical arteries, the end-diastolic flow velocities depend on the volume of the foetoplacental vessel tree, i.e. higher resistance indices (RI) are found in the arteria with the smaller placental area. If there is only one umbilical artery, the peripheral resistance is reduced to 50%, because the part of the placenta part belonging to this solitary umbilical artery is twofold compared to cases with two umbilical arteries. This leads to a higher perfusion pressure gradient with higher flow velocities and lower RI values, resulting in an underestimation of the foetoplacental resistance. In cases of thrombosis of chorionic membrane vessels or stem villi vessels, placental regions are excluded from the perfusion, followed by an increasing foetoplacental resistance in the same manner as it happens in slowly developing failures of villus maturation. This means that the presented cases of umbilical cord anomalies and function disorders of allantois vessels can be interpreted as an in-vivo model to show pressure and resistance parameters in foetoplacental circulation.