Umbilical cord thrombosis is a rare complication of pregnancy and childbirth, which is difficult to detect by routine prenatal examination, but can lead to adverse perinatal outcomes. Umbilical artery thrombosis is more rare.Oppenheimer EH, Esterly JR, retrospectively analyzed perinatal autopsies and found that the incidence of cord blood duct thrombosis was 3/4000[4]. The prospective study by Stephen A. Heifetz showed that the incidence of umbilical cord thrombosis in perinatal live births was 1/1300, and the incidence of umbilical cord thrombosis in high-risk pregnancies was 1/250, with A higher incidence in male fetuses. Umbilical vein thrombosis is more common than single or double umbilical artery thrombosis. Umbilical vein thrombosis was present in 85% of cases, incidence umbilical of umbilical vein thrombosis alone was 62%, combined with single or double umbilical artery thrombosis was 23%. Arterial thrombosis without venous thrombosis was present in
only 15% of cases[5]. Ying Zhu's case analysis of 10 cases of umbilical cord thrombosis in the third trimester of pregnancy showed that umbilical cord structural dysplasia, maternal coagulodysfunction, vascular endothelial damage, elevated blood glucose, and intrauterine transfusion can all lead to thrombosis[6]. Abnormal umbilical cord, such as excessive distortion (> 0.3cm/ loop), presence of true knot, excessively long umbilical cord (> 70cm) or too short umbilical cord (< 35cm), umbilical cord around the body or neck, abnormal placental insertion can cause mechanical compression of vascular access and vasodilatation, which can lead to thrombosis[7]. .Roopali V. Donepudi, in his report of umbilical artery thrombosis after multiple intrauterine transfusions, noted that good pregnancy outcomes when umbilical artery thrombosis occurs depend on the presence of placental Hyrtl branches. The Hyrtl branch is the communication branch between umbilical arteries on the surface of placenta, which exists in 95% of placentas and was discovered and proposed by Joseph Hyrtl in 1870. It balances the blood pressure between different parts of the placenta supplied by the umbilical artery and improves placental tolerance when one artery is blocked[8]. Although venous thrombosis is more common, adverse pregnancy outcomes such as fetal growth restriction and even stillbirth are more common in umbilical artery thrombosis, with most clinical manifestations being complaints of reduced fetal motility with nonreactive NST tests [6]. Timely detection and monitoring are important for good pregnancy outcomes. The case report of Ali Alhousseini showed that prenatal ultrasound diagnosis of umbilical artery was reduced to a single indication of umbilical artery thrombosis, and close follow-up could avoid adverse perinatal outcomes such as stillbirth[8]. Planned cesarean section is an effective method to obtain better pregnancy outcome. The study of umbilical artery thrombosis in 7 cases of CHRISTINE SHILLIN has shown that the formation of umbilical artery thrombosis is not necessarily related to the formation of maternal thrombosis[10]. Similar studies have shown that severe IUGR and end-diastolic loss of umbilical artery blood flow signal indicate umbilical artery thrombosis[11]. Sato and K. Benirschke found in the pathological study of 11 cases of umbilical artery thrombosis that the umbilical artery thrombosis was mainly manifested as partial necrosis of the vessel wall, without villous sclerosis and villous necrosis. This histological change can only be observed in umbilical artery thrombosis. In most umbilical arteries only the inner layer is necrotic and the outer layer is unaffected. This is because the umbilical artery lacks blood vessels that nourish the blood vessels, and nutrients are obtained from the blood and amniotic fluid that flow inside the vessels. Thrombus can lead to necrosis of the inner layer of blood vessels, while oxygen supply from amniotic fluid keeps the outer layer intact[12]. Huanxi L, in two pathological reports of umbilical artery thrombosis, proposed that the characteristic ultrasound sign of umbilical artery thrombosis was "one hand holding an orange sign" at the level of the fetal bladder, because the occluded artery was parallel to the remaining artery and surrounded by uterine veins. It is a good way to distinguish developmental single umbilical artery from secondary umbilical artery thrombosis[13]. According to Virchow's hypothesis, thrombosis is associated with three risk factors: hypercoagulability, endothelial damage, and impaired circulation[14]. Protein S, protein C, antithrombin III defects, factor V mutations and antiphospholipid antibody syndrome can lead to thrombosis. While ischemia-reperfusion (ischemia, tissue hypoxia, fresh blood reperfusion) damages the vascular endothelium, which attracts white blood cells and platelets, and subsequently produces fibrin. Impaired blood flow pulsatility often leads to thrombus[14].