<p>Current Perspectives of Prenatal Sonographic Diagnosis and Clinical Management Challenges of True Knot of the Umbilical Cord</p>

Abstract

Umbilical cord accidents preceding labor are rare. Single and multiple nuchal cords, and true knot(s) of the umbilical cord, are often incidental findings noted at delivery of nonhypoxic non-acidotic newborns without any evidence of subsequent adverse neonatal outcome. In contrast to single nuchal cords, true knots of the umbilical cord, which occur in between 0.04% and 3% of all deliveries, have been associated with a reported 4 to 10 fold increased risk of stillbirth. First reported with real-time ultrasound, current widespread application of color Doppler, power Doppler and three-dimension sonography, has enabled increasingly more accurate prenatal sonographic diagnoses of true knot(s) of the umbilical cord. Reflecting the inability to visualize the entire umbilical cord at prenatal ultrasound assessment, despite detailed second and third-trimester scanning, many occurrences of incidental true knot of the umbilical cord remain undetected and are noted only at delivery. Although prenatal sonographic diagnostic accuracy is increasing, false positive sonographic diagnosis of true knot of the umbilical cord cannot be ruled out with certainty, and must continue to be considered clinically. Notwithstanding the inability to diagnose all true knots, currently there is a clear absence of clinical management guidelines by governing bodies regarding patients in whom prenatal sonographic diagnosis of true knot(s) of the umbilical cord is / are suspected. As a result, in many prenatal ultrasound units, suspected sonographic findings suggestive of or consistent with true knot of the umbilical cord are often disregarded, not documented, and patients are not uniformly informed of this potentially life-threatening condition, which carries an associated considerable risk of stillbirth. This commentary will address current perspectives of prenatal sonographic diagnostic and management challenges associated with true knot(s) of the umbilical cord in singleton pregnancies.

<p>Current Perspectives of Prenatal Sonographic Diagnosis and Clinical Management Challenges of Nuchal Cord(s)</p>

“…For these, the reader is referred to our Commentary published in this journal in 2020, regarding current perspectives of prenatal sonographic diagnosis and clinical management challenges of true knot of the umbilical cord. 6 The umbilical cord may be correctly viewed as an extension of the fetal cardiovascular system. It is important to recognize that the umbilical vessels (both arteries and vein) are protected by unique inherent anatomical features of the umbilical cord, including the length of the umbilical cord, Wharton's jelly, the presence of two arteries, coiling, and suspension in amniotic fluid, which all contribute to protective buffering of the cord from twisting, shearing, and compressive forces throughout gestation, and especially during labor and delivery.…”

“…Predisposing factors of nuchal cord(s) and a true knot(s) of the umbilical cord are similar and include an excessively long umbilical cord (prone to entanglement) and the presence of each of these entities (separately, and at times coexisting in the same pregnancy). 6,[10][11][12][13][14][15][16] Accordingly, predisposing risk factors include excessively long umbilical cords, polyhydramnios, excessive fetal movements, gestational diabetes, multiparity, post-term pregnancy, marginal cord insertion, and male fetuses. 6,[10][11][12][13][14][15][16] Ogueh et al, in a 2006 study of 57,853 singleton deliveries, noted 13,717 deliveries (23.71%) with a least one nuchal cord and additional risk factors, including induction of labor, slow progress of labor, and shoulder dystocia.…”

“…For these, the reader is referred to our Commentary published in this journal in 2020, regarding current perspectives of prenatal sonographic diagnosis and clinical management challenges of true knot of the umbilical cord. 6 …”

“…It is important to recognize that the umbilical vessels (both arteries and vein) are protected by unique inherent anatomical features of the umbilical cord, including the length of the umbilical cord, Wharton’s jelly, the presence of two arteries, coiling, and suspension in amniotic fluid, which all contribute to protective buffering of the cord from twisting, shearing, and compressive forces throughout gestation, and especially during labor and delivery. 6 An additional protective mechanism from the potential effects of compression upon the umbilical arteries is the presence of a 1.5–2 cm shunt between the umbilical arteries within 3 cm of the placental cord insertion, the Hyrtl anastomosis, which is present in approximately 96% of umbilical cords. 7 This arterial anastomosis equalizes pressures between the respective umbilical arteries before entering the placenta and functions as a safety valve in the event of placental compression or blockage of an umbilical artery, and has been confirmed with prenatal ultrasound.…”

“… 6 , 10 - 16 Accordingly, predisposing risk factors include excessively long umbilical cords, polyhydramnios, excessive fetal movements, gestational diabetes, multiparity, post-term pregnancy, marginal cord insertion, and male fetuses. 6 , 10 - 16 Ogueh et al, in a 2006 study of 57,853 singleton deliveries, noted 13,717 deliveries (23.71%) with a least one nuchal cord and additional risk factors, including induction of labor, slow progress of labor, and shoulder dystocia. 14 In general, an umbilical cord length of >70–80 cm is considered a predisposing factor for the formation of nuchal cord(s).…”