Thrombosis of umbilical vessels is a rare occurrence, but it is insidiously associated with perinatal morbidity and mortality. According to Heifetz [1], umbilical vascular thrombosis occurs in around 0.08% of deliveries, 0.1% of postpartum autopsies, and 0.4% of high-risk pregnancies. Avagliano [3] reported that up to 10% of 317 spontaneous intrauterine fetal demise cases were caused by thrombosis of umbilical cord vessels. Our hospital is the largest specialized maternity and children's hospital and the treatment center for critical and severe patients in southwest China and has accumulated a lot of case data of patients with umbilical cord thrombosis. The overall incidence of umbilical cord thrombosis was 0.05% (66/123,746), but the incidence increased significantly in the last 2 years, reaching 0.19% in 2021, which entails that such a significant number should be taken seriously.
The pathogenesis of umbilical vascular thrombosis has not yet been fully comprehended. This may be caused by hypercoagulable mechanical injury or abnormal anatomy of the umbilical cord. A pregnant woman’s blood is hypercoagulable, and the risk of thrombosis increases from four to five times in pregnancy compared with the nonpregnant cohort [4]. Previous studies showed that when maternal blood glucose levels were unstable, the imbalance in the expression of endothelial vasodilatation factors and shrinkage factors were induced, causing disorder of blood coagulation and the eventual occurrence of blood clots. Zhu [5] demonstrated that 5 out of 10 patients with umbilical cord thrombosis had elevated blood sugar levels, 2 had hypertension, and 2 had hypothyroidism. In our series, 11 out of 66 patients had elevated blood sugar levels, 2 had hypertension, and 6 had hypothyroidism. Elevated blood glucose may lead to the formation of thrombosis; therefore, attention should be prioritized on predisposition and precaution.
Previous studies [6, 7] showed that cord anomalies might induce flow stasis and thrombosis of the umbilical cord, such as marginal/velamentous insertion, long umbilical cord, short cord, excessive twisting, reduced diameter, and presence of true knots. Sato [8] reported that 82% of patients with umbilical arterial thrombosis were associated with an abnormal umbilical cord. In this study, the gross examination of the placenta and cord revealed that 26 patients (39.4%, 26/66) had umbilical cord abnormalities. Matsumoto [9] reported that umbilical vein varix was associated with thrombosis in the varix.
The patient does not have typical clinical signs and symptoms; therefore, it is difficult to detect prenatally. The main manifestation was decreased or disappeared fetal movement. In this study, 20 patients had severe adverse pregnancy outcomes of intrauterine stillbirth due to neglected fetal movement, or fetal movement significantly reduced or even disappeared before the patient came to the hospital. The umbilical cord comprises one umbilical vein and two umbilical arteries protected by Wharton jelly. In recent decades, prenatal care has significantly improved, and the evolution of ultrasound imaging has been key in this advancement. When one of the umbilical arteries is embolized, arterial blood flow is blocked; a single umbilical artery of the cord is easily misdiagnosed by an ultrasound examination. Obstetricians should be vigilant if ultrasound imaging shows suspected umbilical vascular thrombosis or shows one umbilical artery when previously two were seen. In this study, five patients were misdiagnosed with a single umbilical artery on prenatal ultrasound. The importance of self-counting fetal movement should be emphasized to patients, and the prenatal diagnosis of umbilical artery thrombosis remains a clinical challenge.
Fetal death has been found to occur rapidly after an abnormal fetal NST result. Many studies believed that a cesarean section should be performed without delay [10, 11, 12]. In this study, 20 patients underwent emergency cesarean section due to decreased fetal movement and unresponsive fetal monitoring; all neonates were alive, with 2 neonates having a 1-min Apgar score of ≤3 and 6 neonates having a 1-min Apgar score of ≤7. The fetus should be closely monitored and interventions implemented as early as possible to improve the prenatal detection rate of umbilical vessel thrombosis and avoid adverse pregnancy outcomes. The fetus should be closely monitored and interventions implemented as early as possible to avoid adverse pregnancy outcomes. However, sudden fetal death could still occur without any foretelling signal. For the patients with umbilical artery thrombosis suspected by ultrasound, determining how often the examination should be performed to find the best term for the termination of pregnancy before the onset of fetal distress or death is controversial. Especially in the case of early preterm, ultrasonographic scans are required weekly from diagnosis to 28 weeks, fetal cardiac monitoring along with the scans are required twice a week thereafter, and elective delivery by cesarean section is required following antenatal corticosteroid therapy for fetal lung maturation.
Umbilical vein thrombosis is more common than umbilical artery thrombosis, but umbilical artery thrombosis is associated with increased fetal and perinatal morbidity and mortality. Heifetz [1] reported that venous, venous and arterial, and arterial thromboses occurred in 70%, 20%, and 10% of patients, respectively. This study showed that venous, venous and arterial, and arterial thromboses occurred in 74.2%, 12.1%, and 13.6% of patients, respectively, and the probability of intrauterine fetal death was 25.6%, 87.5%, and 22.2%, respectively. This study showed that umbilical venous and arterial thromboses were more likely to lead to adverse pregnancy outcomes.
Nevertheless, this study had several limitations. First, this is a retrospective analysis; a large sample and comparative studies should be analyzed to get a more comprehensive understanding of umbilical vessel thrombi. Second, the long-term follow-up of neonates is inadequate. Thus, we could not evaluate survival rates and long-term implications of babies born with umbilical cord thrombosis. However, the data in this study permitted a general assessment of the clinical characteristics and perinatal outcomes of umbilical cord thrombosis.