RESUMEN
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, pathophysiology, 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 increased risk of obstetric intervention and neonatal outcomes because most are loose. However, true knots can tighten during pregnancy due to fetal movement or during labour, leading to reduced blood flow and consequent fetal asphyxia and death. Thus, the close monitoring of pregnancy in cases of true knot of umbilical cord is required. Prenatal diagnosis of true knot of the umbilical cord can be a challenge. Ultrasound complementary techniques, including color Doppler and Doppler velocimetry 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, and consequences for the fetus and newborn.