INTRODUCTION
The occurrence of a true knot of the umbilical cord is very rare.[1] It may be defined as a complete entwining of a segment of the umbilical cord, usually without obstructing fetal circulation and commonly results from fetal slippage through a loop of the cord. Despite the reported incidence of true knots of the umbilical cords ranging from 0.3% to 2.1%, certain factors have been noted to increase its predisposition. These include long umbilical cords,[23] polyhydramnios,[2] small size fetuses,[23] male fetuses, gestational diabetes mellitus, monoamniotic twins, the process of undergoing genetic amniocentesis,[4] and multiparity.[5] Most obstetricians are often concerned and perplexed about the exact time of formation of a true knot of the umbilical cord. In general, the belief is that the true knot of the cord is formed between 9 and 12 weeks of gestation.[1] Early gestation is a period where the amniotic fluid volume is relatively large.[1] Paradoxically, there is reported evidence of knot formation of the umbilical cord when a woman is undergoing labor.[6] In a large number of cases, true knots of the umbilical cord occur without any adverse effect on the fetus. However, sometimes there is an association between true umbilical cord knots and intrauterine fetal death (IUFD). This was seen in both the patients presented here.
CASE REPORT 1
Patient Mrs. ABC, 25 years old, booked primigravida with 35 weeks of pregnancy, with a complaint of absent fetal movements since the previous day evening. The index pregnancy was desired and spontaneously conceived. There were no maternal high-risk factors. The pregnancy was essentially uneventful and ultrasound done at 31 weeks of pregnancy revealed normal findings, with a single loose loop of cord around the neck.
On examination, the patient was a febrile, no icterus, and no pallor. Her pulse was 100–110 bpm and blood pressure (BP) was 110/70mm Hg. The symphysio-fundal height was 32cm. The lie was longitudinal, cephalic presentation, and 4/5 palpable per abdomen. The fetal heart sounds were absent. A vaginal examination revealed an unfavorable cervix. Ultrasound is suggestive of 32 weeks and 2 days of the single intrauterine fetus, longitudinal lie with cephalic presentation. Placenta was anterior, liquor was adequate, and fetal heart movements were absent. Thus, the scan was suggestive of intrauterine fetal demise. The patient counseled and admitted for induction of labor. On admission, her hemoglobin was 12.7g/dL, blood group B Rh positive, and other serology reports were nonreactive. Her liver and kidney function tests were within normal limits.
Induction of labor was done and the patient had an uneventful vaginal delivery. A male baby weighing 1.9kg was delivered. No gross abnormalities were seen. The examination of the fetus showed two tight loops of cold around the neck and the presence of “true knot” [Figure 1]. Minimal peeling of skin was present on the fetal scalp. The placenta was normal; no retroplacental clots were seen. The length of the umbilical cord was around 50cm with true knot present approximately 7cm distal to fetal insertion. The placenta was sent for histopathological examination and revealed features suggestive of infarct placenta along with umbilical cord anomaly (two vessel cords = one artery, one vein). The patient, though advised, did not get the anomaly scan done in the second trimester.
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Figure 1: Two tight loops of cord and true knot with dead fetus
CASE REPORT 2
Patient Mrs. XYZ, age 21 years, booked, gravida 2 with previous cesarean section 3 years back with 24 weeks of gestation came to a casualty with complaints of pain abdomen for 4–5h. No maternal high-risk factors were noted. The last scan was of 13.4 weeks with a nuchal thickness of 1.6mm and nasal bone was seen. Liquor was adequate and the placenta was posterior.
On examination, the patient was a febrile, mild pallor present, and not icteric. Her pulse was 90 bpm and BP was 130/80mm Hg. Per the abdomen, the uterus was 24 weeks size and no fetal heart sound was present. Patients had active 2–3 uterine contractions in 10min lasting for 30s each. On vaginal examination, the cervix was 4cm dilated and 50% effaced with bulging membranes. The patient was counseled and admitted. On admission, her hemoglobin was 9.5 g%. Her liver function and kidney function tests were normal. The patient underwent spontaneous vaginal delivery and delivered a stillborn male fetus of 635g.
Examination of the fetus revealed no gross fetal abnormalities with the presence of a true knot of umbilical cord approximately 10cm distal to fetal insertion. Minimal peeling of fetal skin was present. The placenta was normal and no retroplacental clots were seen. The umbilical cord was 60cm with the presence of a true knot [Figure 2].
Figure 2: True knot of umbilical cord and placenta, with fetal parts seen
DISCUSSION
The diagnosis of a true knot in the umbilical cord during the antenatal period has not been commonly reported in the literature. True knots may arise from the movements of the fetus in utero. In early gestation, this event is more likely to develop because of greater fetal movements and relatively more amniotic fluid. True knots also show an association with advanced maternal age, multiparity, more in male fetuses, and long umbilical cord. The average umbilical cord is 50–60cm long, with a diameter of 1.2cm and 11 helices. The short cord is <35cm and the long cord is >80cm. Both long and short cords are related to different complications. True knots are difficult to diagnose antenatally. This is because true knots are reported to form in all three trimesters.[67] The complete length of the umbilical cord is not routinely seen on ultrasonography (USG). Also, during the third trimester, parts of the cord may be concealed by the fetus. Hence, the USG is not reliable for the diagnosis of the true knot. The “the four-leaf clover” pattern has been described as a characteristic ultrasound feature of the true knot;[89] this pattern is thought to represent two cord segments in a fixed relationship crossing and lying in close proximity to each other. The use of color Doppler USG can identify the true knot, as a bizarre multicolored pattern on color flow imaging, which probably represents superimposed, multidirectional pulsatile arterial and continues venous flow of different velocities. This pattern is not present in false knots or multiple loops of cord. However, further experience is needed to confirm the diagnostic value of this color flow pattern.
Once a prenatal diagnosis of a true knot is suspected, it appears prudent to embark on fetal surveillance by umbilical artery Doppler velocimetry. The detection of umbilical cord knots per se is not an indication of termination of pregnancy unless associated with evidence of fetal compromises, such as abnormal fetal heart patterns.[1011] The routine USG surveillance of the umbilical cord, for the true knot, does not seem justifiable since highly time-consuming. Cesarean delivery may be considered if a diagnosis of a true knot is made and the fetus is alive and viable. In a patient with IUFD, vaginal delivery is more appropriate unless there is an obstetric indication for cesarean section.
The majority of knots seem to be protected against occlusion by the greater thickness of Wharton’s jelly and the large cord radius at this gestational age. If loose, a true knot will not lead to fetal compromise as fetal circulation is maintained.[178] However, by the time of fetal descent through the birth canal, the knot could be tightened. The tightening knot can occlude fetal circulation, resulting in IUFD. Therefore, the Wharton’s jelly surrounding the fetal vessels has the potential of withstanding significant torsional and compressional forces. Occasionally, adequate Wharton’s jelly may not develop in all segments of the cord. When this occurs, fetal vessels are no longer protected from torsional forces and they are prone to occlusion if twisted sufficiently, leading to fetal demise in utero.[17] In this case report, both the fetuses died in utero. This may suggest that the cause of death may have been the presence of true knot obstructing the blood supply. Other possible reasons for the fetal demise could not be identified.
A nuchal cord is defined as an umbilical cord that passes 360° around the fetal neck. The prevalence at delivery has been reported as being between 6% and 37%.[12] The diagnosis of a nuchal cord is not routinely made until delivery; however, it may be suspected prior to delivery due to the presence of variable decelerations in the fetal heart rate of the cardiotocograph (CTG) during labor.[12] With the improvement of ultrasound machines, the detection rate of the nuchal cord is increasing steadily. One cord loop is reported in 20%–34% of deliveries, two loops in 2.5%–5%, and three loops in 0.2%–0.5%.[13] Despite their frequency, nuchal cords are a relatively uncommon cause of adverse perinatal outcomes.
CONCLUSION
Prenatal diagnosis of a true knot of the umbilical cord has been infrequently reported in the literature. It is difficult to diagnose even with USG. Hence, routinely USG is not advisable for screening for the true knot. Many patients with true knots deliver normally. However, if an incidental finding of a true knot is made remote from term, prenatal counseling should be done. The patient will need strict cardiotocographic monitoring if she goes into labor. As explained earlier, the true knot is not an indication for the cesarean section but the cesarean section may be contemplated if the fetus is viable. However, in both cases, IUFD was associated with the presence of a true knot. The condition could not be diagnosed by USG. The unexpected sudden death of the fetus places the obstetrician in an embarrassing situation. He/she finds it difficult to explain, why true knot could not be diagnosed before the death of the fetus.
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Conflicts of interest
There are no conflicts of interest.
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