True Knot of Umbilical Cord: A Diagnosis and Prognostic Challenge

Abstract

Introduction: True knot of the umbilical cord is characterized by a cord loop with increased tension and hence higher risk for obstetric and neonatal outcome intervention. It is a finding observed in 1-2% of births. Aim: Review the etiology, physiopathogeny, diagnosis and prognosis of true knot of the umbilical cord. Methodology: We carried out a review searching for scientific articles present in the electronic database PubMed, using the descriptors "true knot", "umbilical cord", "Doppler sonography" and "prenatal diagnosis". Articles published until 2013 were included in the review. Discussion: True knot of the umbilical cord is a relatively common finding at birth. However, its diagnosis in uterus is still quite rare. Several factors have been related to its etiology, including the size of the umbilical cord. Its appearance occurs mostly between 9 and 28 weeks of gestation, in the fetal period of greater mobility. The major part of the true knot of the umbilical cord is not associated to an increased risk of obstetric intervention and neonatal outcomes because most are loose. However, the true knots can tighten during pregnancy due to fetal movement or during labor, leading to reduced blood flow and consequent fetal asphyxia and death. As a result, the close monitoring of pregnancy in cases of true knot of umbilical cord is required. The prenatal diagnosis of a true knot of the umbilical cord can be a challenge. Sonographic complementary techniques, including color Doppler and Dopplervelocimetry can improve the detection rate and help to differentiate true from false knots. And this has important implications for the management and prognosis of pregnancy, besides consequences for the fetus and newborn.

Umbilical Cord Abnormalities and Pregnancy Outcome

“…Umbilical cord knots are either true or loose. True knots are observed in 1-2% of all births worldwide and are characterised by variable degrees of increased tension which can potentially compromise blood flow through the cord and increase the risk of abnormal foetal heart rate pattern and interventions in labour so, careful monitoring of pregnancy with true knot of the cord is essential [35]. It has been also estimated that true knot of the cord is associated with fourfold increase in the risk of foetal death [36].…”

“…Loose knots may become tight due to foetal movements, or during descent of the baby in labour. But, as long as they remain loose, they are considered of minor importance [35].…”

“…Nevertheless, in the majority of cases, it may not be identified by ultrasound and remains a postnatal finding. The limitations of prenatal diagnosis are mainly due to difficult examination of the entire length of the cord and poor identification of the characteristics of the knot in two dimension scan [35].…”