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

Abstract

A true knot of the umbilical cord (TKUC) is an actual knot formed in pregnancy. It is seen in approximately 0.3%-1.2% of all pregnancies. True knots are of significance as they can cause a wide spectrum of adverse perinatal outcomes like small for gestational age (SGA) fetus, low appearance, pulse, grimace, activity, and respiration (Apgar) score at birth, fetal hypoxia, and even fetal demise. Here, we report a case series of three patients with TKUC and the varied adverse perinatal outcomes associated with them. A low-risk primigravida at term gestation had a suspicious non-stress test (NST). Repeat NST after maternal resuscitation became pathological. Emergency cesarean delivery was performed in view of pathological NST persisting despite intrauterine resuscitation. A healthy male baby weighing 2920 g was delivered, and the umbilical cord had a true knot. A multigravida at 33 + 3 weeks of gestation was referred with fetal growth restriction (FGR). Color Doppler examination showed absent end-diastolic flow (AEDF) in the umbilical artery (UA). Cesarean delivery was performed in view of FGR stage two with AEDF in the UA at 34 weeks of gestation as per the Barcelona criteria. A male baby weighing 1505 g was delivered. The umbilical cord had a true tight knot. The baby had an Apgar score of 7 at one minute after birth but was shifted to the neonatal intensive care unit (NICU) in view of low birth weight and prematurity. The baby slowly gained weight and was discharged from NICU after 15 days in stable condition. A multigravida at 32 weeks of gestation was referred with intrauterine fetal demise. Ultrasonography confirmed the presence of a single intrauterine dead fetus corresponding to 30 + 4 weeks of gestation with an estimated fetal weight (EFW) of 1633 g, amniotic fluid index (AFI) equal to nine, and presence of Spalding's sign. Induction of labor was done, and she expelled a dead macerated male fetus weighing 1825 g. The infantogram was normal. A true umbilical cord knot was found. The umbilical cord is the source of fetal blood supply; therefore, any cord abnormality can have a significant impact on the fetal outcome. There are various factors that can predispose to TKUC, such as polyhydramnios, increased cord length, monoamniotic twins, male baby, grand multiparity, small fetus, and amniocentesis. TKUC can lead to various adverse outcomes in pregnancy and labor like SGA fetus, low Apgar score at birth, fetal hypoxia, and fetal demise. TKUC increases the risk of fetal demise by as much as four times. With the development of advanced techniques such as three-dimensional/four-dimensional color Doppler ultrasounds, TKUC can be diagnosed antenatally in the form of a four-leaf-clover, a "hanging-noose sign," or by an unusual multicolor pattern in the cord. The prenatal detection rate of TKUC is only 12%. It mostly remains undetected unless visualized incidentally. Although TKUC is not rare and can have serious outcomes, the importance of its antenatal diagnosis has not been determined. It should be suspected in patients with risk factors, and emphasis should be placed on its antenatal diagnosis on ultrasonography to avoid obstetric disasters in otherwise low-risk females. Though there is no specific management of these cases, a good clinical outcome can be achieved if TKUC is diagnosed antenatally and monitored closely until fetal maturity is attained.

Keywords: adverse perinatal outcomes; human umbilical cord; perinatal mortality; perinatal outcome; true knot.

Figure 1. Admission non-stress test (NST) showing baseline fetal tachycardia

Figure 2. Repeat NST showing persistent fetal tachycardia with multiple spontaneous decelerations

Figure 3. True knot of umbilical cord

Figure 4. Absent end-diastolic flow in the umbilical artery on Doppler ultrasonography

Figure 5. Tight true knot in umbilical cord

Figure 6. Dead macerated male baby

Figure 7. Normal infantogram of the baby

Figure 8. Placenta with a true knot in the cord