To evaluate the value of prenatal 3D high resolution simulated blood flow mapping by color Doppler ultrasonography in the evaluation of true umbilical cord knots.

A total of six fetuses with umbilical cord knots were diagnosed at the Department of Ultrasound, Beijing Obstetrics and Gynecology Hospital from January 2019 to June 2019, and all of them were confirmed after delivery. All cases were examined by two-dimensional ultrasound and color Doppler ultrasonography. When the umbilical cord was suspected to be knotted, 3D high resolution simulated blood flow mapping was performed. The imaging findings were then analyzed.

Among the six cases, one was single chorionic and single amniotic sac twins, and the other five were singletons; five were pregnant after cesarean section and one was delivered naturally. The umbilical cords of the one single chorionic and single amniotic sac twins were wound around each other to form a double "8" complex knot similar to Chinese knot, and the five singleton fetuses showed single "8" knot features. Two cases were associated with local thickening of the umbilical cord, edema, and umbilical cord cyst, and one case was complicated with umbilical vein thrombosis.

For patients with suspected umbilical cord knotting and high risk factors, it is necessary to carefully observe the umbilical cord to reduce the missed diagnosis of true umbilical cord knots, and 3D color Doppler high resolution simulated blood flow technique can stereoscopically and intuitively display the morphological structure and blood flow of the umbilical cord, which is helpful to determine the diagnosis of true umbilical cord knots.