Current Perspectives of Prenatal Sonographic Diagnosis and Clinical Management Challenges of True Knot of the Umbilical Cord

Knots of the umbilical cord: Incidence, diagnosis, and management

Knot(s) of the umbilical cord have received emphasis because the clinical assessments and sonographic literature show a crucial role in fetal outcomes. The true umbilical cord knot could be a knot in a singleton pregnancy or an entanglement of two umbilical cords in monoamniotic twins. Clinical manifestations are almost silent, which can raise clinical challenges. They worsen outcomes, and the pathology can be easily missed during prenatal visits because ultrasonographers do not pay attention to the cord during an obstetric ultrasound scan. However, most medical centers now have ultrasound machines that improve fetal assessment. The umbilical cord should be routinely evaluated during a fetal assessment, and suspicion of an umbilical cord knot can be more frequently diagnosed and is detected only incidentally. Clinical outcome is usually good but depends on the knot's characteristics and if it is tight or loose. In this review, we discuss pathophysiology, the theories on formation, the main risk factors, ultrasound signs and findings, different opinions in the management, and features of pregnancy outcomes feature.

Clinical significance of true umbilical cord knot: a propensity score matching study

OBJECTIVE

True umbilical cord knot (TUCK) is a rare finding that often leads to intensified surveillance and patient anxiety. This study sought to evaluate the incidence, risk factors, and obstetric and neonatal outcomes of TUCK.

METHODS

A retrospective cohort study was conducted at a tertiary university medical center in 2007-2019. Patients with singleton pregnancies diagnosed postnatally with TUCK were identified and compared to women without TUCK for obstetric and neonatal outcomes using propensity score matching (PSM).

RESULTS

TUCK was diagnosed in 780 of the 96,766 deliveries (0.8%). Women with TUCK were older than those without TUCK (32.57 vs. 31.06 years, P < 0.001) and had higher gravidity (3 vs. 2, P < 001) and a higher rate of prior stillbirth (1.76% vs. 0.43%, P < 0.01). Following covariate adjustment, 732 women with TUCK were compared to 7320 matched controls. TUCK was associated with emergency cesarean delivery due to non-reassuring fetal heart rate (2.54% vs. 4.35%, P = 0.008, OR 1.71, 95%CI 1.14-2.56) and intrapartum meconium-stained amniotic fluid (19.26% vs. 15.41%, P = 0.022, OR 1.31, 95%CI 1.04-1.65). Neonatal outcomes were comparable except for higher rates of 1-min Apgar score < 7 and neonatal seizures in the TUCK group. The stillbirth rate was higher in the TUCK group, but the difference was not statistically significant (1.23% vs 0.62%, P = 0.06, OR 1.96, 95%CI 0.96-4.03).

CONCLUSIONS

TUCK has several identifiable risk factors. Pregnant women with TUCK may cautiously be informed of the relatively low risks of major obstetric or perinatal complications. The lower occurrence of stillbirth in the TUCK group warrants further study.

Pregnancy and umbilical cord pathology: structural and functional parameters of the umbilical cord

Scientific research in the field of physiology and pathology of the umbilical cord is quite limited and imperfect. The purpose of the study was to evaluate the histological architecture of the pathological umbilical cord and investigate the relationship between the main parameters and placental postnatal macromorphometric characteristics, which serve as a reflection of placental dysfunction. Four groups of patients were included, each undergoing a postnatal histological and topographic examination of the umbilical cord: Wharton's jelly edema (10 samples), velamentous cord insertion (10 samples), single umbilical artery (10 samples), and physiological pregnancy (10 samples). Compared to the control group, all newborn groups exhibited changes in umbilical vessel morphology, characterized by an increased Wagenworth index and a decreased Kernohan index. The functional indices of the umbilical vessels were found to be most severely affected in cases of Wharton's jelly edema. In cases of single umbilical artery, the changes in vascular functional parameters indicated their compensatory remodeling with the highest Wagenworth and Kernohan indices of the umbilical vein. Deviation from the normal average placental weight was observed in cases of Wharton's jelly volume pathology or velamentous cord insertion. However, in the case of a single umbilical artery, there were no significant deviations in the macromorphometry of the placenta.

True Knot of the Umbilical Cord and Associated Adverse Perinatal Outcomes: A Case Series

An actual knot that forms during pregnancy is known as a true knot of the umbilical cord (TKUC) which is seen in 0.3% to 1.2% of pregnancies. TKUC is noteworthy because it can lead to a variety of adverse perinatal outcomes, including infants with low Apgar scores, small for gestational age (SGA) fetuses, fetal hypoxia, and also in some cases fetal death. Here, we present instances of TKUC of three patients and the various associated perinatal outcomes.

Umbilical Cord Knots: Is the Number Related to Fetal Risk?

True knots of the umbilical cord (UC) are a rare occurrence and are reported in 0.4–1.2% of deliveries. The compression of true knot of the UC can cause obstruction of the fetal circulation, leading to intra-uterine growth retardation or fetal death. Predisposing factors for the genesis of the true UC knot are numerous and include all the conditions, which lead to a relatively large uterine volume. This situation may predispose to free and excessive fetal movements. Although not all true knots lead to perinatal complications, they have been associated with adverse pregnancy outcomes, including fetal distress, fetal hypoxia, intra-uterine growth restriction (IUGR), long-term neurological damage, caesarean delivery and stillbirth. We present a rare case of operative delivery with vacuum in a multiparous woman at term of pregnancy with a double true knot of the UC. As in most cases, the diagnosis was made after delivery, as there were no fetal symptoms during pregnancy. Some authors assume that 3D power sonography may be useful in the diagnosis of true UC knots. However, 3D power Doppler cannot be considered as a definitive method. There are no specific prenatal indications to induce the physician to look for ultrasound signs suggestive of umbilical true knot. Some studies argue that cases of fetal death and fetal risk are directly related to the number of knots. We also support this thesis, even if further observational and retrospective studies are needed to demonstrate it.

Current Perspectives of Prenatal Sonography of Umbilical Cord Morphology

The umbilical cord constitutes a continuation of the fetal cardiovascular system anatomically bridging between the placenta and the fetus. This structure, critical in human development, enables mobility of the developing fetus within the gestational sac in contrast to the placenta, which is anchored to the uterine wall. The umbilical cord is protected by unique, robust anatomical features, which include: length of the umbilical cord, Wharton’s jelly, two umbilical arteries, coiling, and suspension in amniotic fluid. These features all contribute to protect and buffer this essential structure from potential detrimental twisting, shearing, torsion, and compression forces throughout gestation, and specifically during labor and delivery. The arterial components of the umbilical cord are further protected by the presence of Hyrtl’s anastomosis between the two respective umbilical arteries. Abnormalities of the umbilical cord are uncommon yet include excessively long or short cords, hyper or hypocoiling, cysts, single umbilical artery, supernumerary vessels, rarely an absent umbilical cord, stricture, furcate and velamentous insertions (including vasa previa), umbilical vein and arterial thrombosis, umbilical artery aneurysm, hematomas, and tumors (including hemangioma angiomyxoma and teratoma). This commentary will address current perspectives of prenatal sonography of the umbilical cord, including structural anomalies and the potential impact of future imaging technologies.

Current Perspectives of Prenatal Sonographic Diagnosis and Clinical Management Challenges of Complex Umbilical Cord Entanglement

Diagnosis of potential umbilical cord compromise, namely, true knots of the umbilical cord and nuchal cords has been enabled with increasing accuracy with current enhanced prenatal sonography. Often an incidental finding at delivery, the incidence of true knots of the umbilical cord has been estimated at between 0.04% and 3% of deliveries. This condition has been reported to account for a 4 to 10-fold increase of stillbirth and perinatal morbidity of 11% of cases. Nuchal cords, commonly observed at the delivery of uncompromised, non-hypoxic non-acidotic newborns occur more frequently with single nuchal cords noted in between 20% and 35% of all deliveries at term. Multiple nuchal cords are considerably less frequent, with decreasing frequencies inverse to the number of nuchal cord loops. While clearly single (and likely double) nuchal cords are almost uniformly associated with favorable neonatal outcomes, emerging data suggest that cases of ≥3 loops of nuchal cords are more likely to be associated with an increased risk of adverse perinatal outcome (either stillbirth or compromised neonatal condition at delivery). We define cases of a true knot of the umbilical cord, cases of ≥3 loops of nuchal cords, any combination of a true knot and nuchal cord, or any umbilical cord entanglement (nuchal or true knot) in the presence of a single umbilical artery, in singleton gestations as complex umbilical cord entanglement. Two concurrent developments, the increase in accuracy of prenatal sonographic diagnosis of complex umbilical cord entanglement and recent data confirming fatal compromise of the umbilical circulation in approximately 20% of cases of stillbirth, suggest that establishing governing body guidelines for reporting of potential umbilical cord compromise, and recommendation of consideration for early-term delivery of select cases, may be warranted. This commentary will address current perspectives of prenatal diagnosis and clinical management challenges of complex umbilical cord entanglement.

Current Perspectives of Prenatal Sonographic Diagnosis and Clinical Management Challenges of Nuchal Cord(s)

Umbilical cord accidents preceding labor are uncommon. In contrast, nuchal cords are a very common finding at delivery, with reported incidences of a single nuchal cord of approximately between 20% and 35% of all singleton deliveries at term. Multiple loops occur less frequently, with reported incidence rates inverse to the number of nuchal cords involved. Rare cases of up to 10 loops of nuchal cord have been reported. While true knots of the umbilical cord have been associated with a 4–10-fold increased risk of stillbirth, nuchal cord(s) are most often noted at delivery of non-hypoxic non-acidotic newborns, without any evidence of subsequent adverse neonatal outcome. Prior to ultrasound, nuchal cords were suspected clinically following subtle (spontaneous or evoked) electronic fetal heart rate changes. Prenatal sonographic diagnosis, initially limited to real-time gray-scale ultrasound, currently entails additional sonographic modalities, including color Doppler, power Doppler, and three-dimensional sonography, which have enabled increasingly more accurate prenatal sonographic diagnoses of nuchal cord(s). In contrast to true knots of the umbilical cord (which are often missed at sonography, reflecting the inability to visualize the entire umbilical cord, and hence are often incidental findings at delivery), nuchal cord(s), reflecting their well-defined and sonographically accessible anatomical location (the fetal neck), lend themselves with relative ease to prenatal sonographic diagnosis, with increasingly high sensitivity and specificity rates. While current literature supports that single (and possibly double) nuchal cords are not associated with increased adverse perinatal outcome, emerging literature suggests that cases of ≥3 loops of nuchal cords or in the presence of a coexisting true knot of the umbilicus may be associated with an increased risk of stillbirth or compromised neonatal status at delivery. This commentary will address current perspectives of prenatal sonographic diagnosis and clinical management challenges associated with nuchal cord(s) in singleton pregnancies.