2002-09-18-10 Umbilical cord anomalies © Jeanty www.thefetus.net/
Umbilical cord anomalies
Fernando Heredia, MD, Philippe Jeanty, MD
Women"s Health Alliance, Nashville, Tennessee.
Ultrasound assessment of the umbilical cord, although not always possible throughout its entire length, may assist in the diagnosis of important congenital and functional anomalies of this structure.
1.1. Abnormal number of vessels
Single umbilical artery (SUA), the most common anatomical abnormality of the umbilical cord, is found in 0,2-1,1% of singleton pregnancies1, and in 6-11% of multiple pregnancies. The selection process of the missing (or existing) vessel is likely to be random, even though a right single artery is slightly more common2. It is frequently found in association with:
- fetal structural anomalies and
- aneuploidies 3,4,5,6.
In early pregnancy the incidence of single umbilical artery is lower than among newborn, due to a possible atrophy of one of the umbilical arteries 3. Malformations among fetuses with single umbilical artery have been reported to be as high as 46%7,8. In a meta-analysis of 37 studies related to single umbilical artery, the mean association with structural anomalies was 27% in liveborn, while in specimens obtained from early abortions, fetal deaths and autopsies it raised up to 66,3%9.
Graphic 1: Organ system anomalies associated with liveborn infants with single umbilical artery. (From Single umbilical artery: visualization , by Lee W. et al.)
Table 1 shows all the reported structural anomalies associated with single umbilical artery 10.
Limb reduction defects11.
Rib and sternal anomalies.
- Renal agenesis.
- Renal hypoplasia or dysplasia.
- Horseshoe kidneys.
- Hydroureter and Hydronephrosis.
- Mullerian duct agenesis or anomalies.
- Wolffian duct agenesis or anomalies.
- Malformed external genitalia.
Esophageal atresia or stenosis.
Omphalocele and gastroschisis.
Neural tube defects.
Single umbilical artery is found in 6,1-11,3% of infants with chromosomal anomalies, mainly trisomies 18 and 135,6. It is rarely a finding of other autosomal trisomies or sex chromosome aneuploidy. In 31% of aneuploid fetuses with single umbilical artery, other structural anomalies are found8. Considering the risk of cardiovascular abnormalities a careful review of the fetal heart is suggested14.
Nevertheless, finding an isolated single umbilical artery is apparently not an indication for fetal karyotype study unless IUGR or other structural anomalies are encountered15,16.
A transverse section of the umbilical cord shows two vessels. Examination of umbilical blood flow with color Doppler may facilitate diagnosis. However, by far the easiest way to assess the number of arteries, is by identifying the intra-abdominal portion of the umbilical artery along side the bladder with color Doppler17,18.
Several combinations of vessels can give the appearance of 4-vessel cords:
Two veins & two arteries
Four-vessels cords result from the persistence of the right umbilical vein. Some reports suggest an increase in congenital anomalies (such as ectopia cordis, atrial septal defect, symmetrical bifid liver, cleft lip and palate, arteriovenous fistulas of the placenta)19,20 while others do not21,22.
One vein & 3 arteries
Another common cause (up to 5% of cords!) for a fourth vessel is the persistence of small vitelline arteries. These rarely exceed 0.5 mm in diameter23. These extra vessels follow the normal twisting of the main umbilical arteries. Actually most of those vessels are actually paired or partially doubled, so that the cord contains on some length 4 arteries. Usually these vessels run for the whole length of the cord. No increase in congenital anomaly was observed.
One vein, two arteries and a duct
While an allantoic (2/3) or omphalomesenteric (1/3) duct remnant is not a true vessel, the ultrasound appearance is difficult to distinguish since flow in such small vessels may not always be detected with either pulsed or color Doppler. At pathology, vestigial remnants with flat epithelium originate from the allantoic duct, while remnants with cuboidal or columnar epithelium originate from the omphalomesenteric duct. The allantoic remnants persist until term while omphalomesenteric duct remnants disappear by mid-gestation23.
The following are two examples of allantoic duct.
This is an example of an omphalomesenteric duct.
Occasionally the incidence of the ultrasound beam gives exquisite view of the vessels walls and gives the impression of extra vessels.
5- and more vessels cords
These are the numerous variations associated with conjoined twining.
Cords with unequal numbers of vessels at the fetal and placental ends
Partial division of the primordial umbilical artery
Occasionally the original primordial umbilical artery fails to divide longitudinally in two umbilical arteries. The division starts at the placental end and extends towards the embryo. These cords will thus present with 3-vessel on the placental end but 2 on the fetal end.
A rare form of unequal number occurs in minimally conjoined twins or in monoamniotic twins that only share part of the cord. Those cords are forked and may have either a single umbilical artery for each twin but may even have normal 3-vessel cords for each twin reduced to a 2-vessel cord at implantation24.
1.2. Abnormal course or connection of vessels
Velamentous insertion of the cord
In velamentous insertion, the cord is not connected to the placental plate, and its vessels travel between the membranes before attaching eccentrically to the placenta. It happens in 1.1% in singleton pregnancies and 8.7% of twins25.
Associated anomalies are found in 5.9-8.5% of cases26,27. These include:
- Esophageal atresia.
- Obstructive uropathies.
- Congenital hip dislocation.
- Asymmetrical head shape.
- Spina bifida.
- Ventricular septal defects.
- Single umbilical artery.
- Bilobate placenta.
- Trisomy 21.
When these out-of-the-cord vessels pass below the presenting part, the condition is called "vasa previa". In such cases, rupture of membranes may tear the vessels apart, causing a fetal hemorrhage.
Vasa previa (2:10,000 pregnancies32) has been associated with bilobed, succenturiate-lobed or low-lying placentas and in-vitro fertilization28,29. Vasa previa can be diagnosed prenatally by ultrasound, ideally transvaginally30, with a specificity around 91%31.
Ultrasound appearance: The diagnosis can be suggested by gray-scale ultrasonography as parallel echogenic or circular lines near the cervix32. Doppler visualization of vessels in close proximity to the internal os allows a definitive diagnosis. 3D-ultrasound has recently been used to complement the gray-scale 2D in order to get axial views of the endocervical canal toward the internal os until the aberrant vessels are seen33.
There is also a short video clip available.
Be aware that flash artifacts resulting from fluid motion from the fetus may mimic the presence of vasa previa.
Management: when the diagnosis of vasa previa made, elective cesarean delivery is advisable before the onset of labor.
Ductus venosus agenesis
Although absence of the ductus arteriosus is very rare34, absence of the venosus is occasionally seen. The return of the umbilical flow is via various vicarious ways 35,36:
- a suprahepatic connection to the inferior vena cava or
- rarely to the right atrium directly 37,38,39,40,41,42,43
- an infrahepatic connection to the inferior vena cava 42,44,45,76
- a cutaneous anastomosis with formation of a caput medusa
- a left 46,47 or right iliac connection.
1: The normal umbilical vein to portal vein with the ductus; 2: the suprahepatic connection to the inferior vena cava; 3: the infrahepatic connection to the inferior vena cava; 4: caput medusa in cutaneous anastomosis; 5: the iliac connection; 6: Connection to the right atrium.
The typical ultrasound finding is that of the absence of the connection of the umbilical vein into the portal vein. The other findings, of course, depend on the type of connection. In the iliac connection, the umbilical flow returns to the iliac vein and thus to the inferior vena cava. The presence of a large inferior vena cava is very suggestive of agenesis of the ductus venosus with vicarious connection to the iliac vein. Check the portal circulation when in doubt.
This is an example of type 3 ductal agenesis, with the umbilical vein joining directly to the inferior vena cava.
This are example of type 6 ductal agenesis, with the umbilical vein joining directly into the right atrium.
You can see these cases also in the following links: Ductus 1, Ductus 2, Ductus 3.
Mostly, few anomalies are associated but cases with:
- Focal liver necrosis39 and calcifications.
- Diaphragmatic hernia49.
- Ureteral obstruction50.
- Facial anomalies.
- Bell-shaped thorax with increased intermamillary distance.
- Muscular hypotonia.
- Hydrops and cardiovascular anomalies51,52,53 have been described.
Probably the most common association is with Noonan syndrome, in particular in cases of ductal agenesis with iliac connection of the umbilical vein54. In cases of congenital absence of the portal vein, the intestinal and splenic venous drainage bypasses the liver and drains directly into the inferior vena cava, the left renal vein, or the left hepatic vein. The superior mesenteric vein may drain into the left renal vein55.
An interesting point of physiology: in fetuses with iliac connection of the umbilical vein, the normal streaming of the flow that occurs in the inferior vena cava is disrupted. That streaming separates the oxygenated and deoxygenated blood that reaches the heart. These fetuses may thus go into cardiac failure and develops hydrops. Fetuses with suprahepatic connections do not develop hydrops56.
Replaced umbilical artery to the superior mesenteric artery
The normal embryology is for the vitelline artery to regress and persist only as the superior mesenteric artery. In this case the left umbilical artery is replaced (which means: improperly connected) to the superior mesenteric artery and the right umbilical artery was in normal position. Replaced umbilical artery to the superior mesenteric artery is very rare in normal fetuses (some may be trisomy 21) but it is common fetuses with defective vascularization (fetus-in-fetu57, acardiac twins and sirenomelia fetuses58,59).
There are several reports of complications resulting from the persistence of both the vitelline artery and veins in adults. As can be expected from the embryology, as the secondary yolk sac involutes and is occasionally detected in adults as a Meckel diverticulum, the persistent vitelline arteries and veins usually become symptomatic because they cause intestinal obstructions60,61,62,63,64,65,66,67,68,69.
You can see some images in this link: Replaced umbilical artery.
Coronary sinus drainage to the umbilical portion of the left portal vein
Coronary sinus connection to the umbilical portion of the left portal vein is an uncommon anomaly since replaced coronary veins usually drain in the portal or splenic veins70.
Persistent right umbilical vein
A right umbilical vein is a relatively common variation (23:10,00073) where the right umbilical vein persists instead of obliterating around 6 weeks as a result from enlargement of the liver. When the first report in the ultrasound literature was made71, the persistent right umbilical vein was noticed mostly because of the presence of the associated anomalies. Up to that report very few cases (less then half a dozen) had been reported in the literature. Since that report however, many others72,73,74 have identified the condition and the association with congenital anomalies (cardiac anomalies 15%, abdominal visceral situs inversus, total anomalous pulmonary venous connection, unilateral renal agenesis, unilateral phocomelia, umbilical vein varix, diaphragmatic hernia, trisomy 1875,76,77,78) has been much less strong then initially though79,80,81. Most authors nowadays consider it as an anatomic variant that is not rare and usually associated with a favorable outcome 81. Persistent right umbilical vein varix has been reported 82, and carries the same management considerations as a normally positioned umbilical vein varix.
The ultrasound appearance is fairly characteristic with the umbilical vein curving towards the stomach instead of parallel to it and the gallbladder often visible midline to the umbilical vein instead of lateral.
There is also a short video clip available.
Management: this anomaly is an indication for conducting targeted fetal sonography and echocardiography. When the persistent right umbilical vein is connected to the portal system and other anomalies are ruled out, the prognosis can generally be expected to be favorable 75.
Arteriovenous fistula between the umbilical vein and the inferior epigastric arteries83 can mimic congestive heart failure in the fetus and newborn.
1.3. Abnormal structure or configuration of vessels
Hypoplastic umbilical artery
A hypoplastic umbilical artery is an artery whose diameter is smaller than the contralateral artery by 1 mm, 30% or 50% depending on the various authors. The differences in diameter usually result in much dramatic difference of cross-section area where the hypoplastic umbilical artery is 2-3 times smaller than the contralateral artery.
The resistance index of hypoplastic umbilical artery is also increased84, but without pathological connotation, simply reflecting a greater resistance due to the small diameter.
Overall this is more a curiosity than an indicator of pathology. Associated anomalies that have been described include85:
- Placental pathology .
- Congenital heart disease.
- Fetal growth restriction.
Being aware of the normally increased resistance in the hypoplastic umbilical artery should be sufficient to not consider it a sign of placental disease86.
These are some hypoplastic umbilical artery images:
Umbilical artery stenosis
Umbilical artery stenosis is a rare condition, almost always found on three vessel cords. There is only one report in which this anomaly was found in a 2-vessel cord of a fetus with Rhesus alloimmunization, which required intrauterine transfusion87. Some authors believe this anomaly may be a consequence of funicular puncture. Pathological specimens show coagulative necrosis, thrombosis, and focal calcification. In those cases it is referred to as "regression" 88.
Thrombosis of an umbilical artery may result from extension of an aortic clot such as may happen in aortic aneurysms89. The occluded artery will appear echogenic and at pathology emboli can be seen in the placenta. Calcified mural thrombi have even been identified in an acardiac fetus90. The anomaly is not necessarily fatal91 in fetuses with 3-vessel cord, but is for fetuses with 2-vessel cords.
Thrombosis of the vein92 is rare and fatal93. It has been reported to occur more frequently in the offspring of diabetic mothers as well as chorionic vessel and perinatal renal venous thromboses94.
As expected, the appearance is that of an echogenic umbilical vein. If fetal death does not occur immediately, nonimmune hydrops fetalis can develop95.
Segmental thinning of umbilical cord vessels
Segmental thinning of umbilical cord vessels results from decrease of the tunica media vasorum (a form of dysplasia of the media) and causes apparent narrowing of the cord. In a series of 17 cases95 it occurred in 1.5% of placenta examined at delivery. The vein is affected in 3/4 of cases, and one or both arteries in 1/4 of the cases. 30% of the fetuses had congenital anomalies, including anencephaly, genitourinary tract abnormalities, and conjoint twins.
Umbilical cord constriction
Umbilical cord constriction can be due to intrinsic or extrinsic mechanisms. Constriction may lead to different degrees of flow limitation in the cord"s vessels, which can be demonstrated by pulsed Doppler flow studies.
Intrinsic constriction is characterized by localized absence of Wharton"s jelly, leading to narrowing of the cord, thickening of the vascular walls and narrowing of the vascular lumens. In this setting, fetal death might occur due to acute vasospasm, acute oligohydramnios and uterine contraction, or an obliterating thrombus96.
Extrinsic constriction can be caused by:
- Amniotic bands97, 98, 99, 100.
- Nuchal loops101.
- True knots 101.
- Fetal grasping101,102.
- Entanglement in monoamniotic twins101.
- Cord presentation and occult prolapse 101.
This is an example of cord presentation
This is an example of cord prolapse
Nuchal cord loops
Single umbilical cord nuchal loops are encountered in 20-33% of normal term pregnancies103. According to Larson, the occurrence of nuchal entanglement increases linearly from 5.8% at 20 weeks of gestation to 29% at 42weeks104. It is slightly more common in male fetuses105. This situation is considered a normal variation and thus, it does not affect pregnancy outcome or fetal weight at birth 105,106. Giacomello classified the nuchal cord into two types107:
Type A - nuchal loop that encircles the neck in a freely sliding pattern
Type B - nuchal loop that encircles the neck in a locked pattern
These are a few examples of nuchal cord entanglement.
Other locations are also frequent, such as the abdomen or the lower lims.
Multiple cord loops are also a frequent event. This is a rare case of quintuple nuchal cord entanglement.
Some cords seem entangled but they are not, and they are called draped around the neck.
Only few reports show some relationship between cord entanglement and adverse maternal or fetal outcome:
-Amniotic fluid embolism (premature placental separation with a marginal tear of the membranes which opens a route of entry for amniotic fluid into the subplacental maternal venous sinuses108).
-Axillary artery postpartum spasm with subsequent limb ischemia109.
Cord-to-cord entanglement in twin gestations
Cord-to-cord entanglement in monoamniotic twin gestations is the rule. It has been associated with growth discordance between the twins and subsequent death of the smaller fetus110,111.
Umbilical vein varix
Umbilical vein varix is an uncommon anomaly17,112,113. Umbilical vein varix may occur in the amniotic fluid or in the intrahepatic portion of the umbilical vein. Most of the time the anomaly is well tolerated but clot may form in the varix. Secondary schistocytic hemolytic anemia may occur due to turbulent flow through the varix and subsequently congestive heart failure114 and fetal hydrops115. Thrombotic occlusion has been reported resulting in fetal death116. Chromosomal anomalies are found in up to 12% of fetuses with this anomaly 115.
Management: Some authors have recommend close fetal monitoring during labor, and delivery when lung maturity has been accomplished or if fetal distress is apparent 98. If hemolytic anemia is suspected, thorough evaluation of the newborn postnatally is advisable for an appropriate diagnosis and treatment 99.
The following images show Umbilical vein varix.
There is also a small video clip available.
Abnormal cord coiling
Normally, the umbilical cord coils to the left. Cord coiling index can be determined by dividing the total number of coils by the length of the cord. Umbilical cord coiling index has been reported to be around 0.21 +/- 0.07 (SD) coils per centimeter117. Prenatally, this is virtually impossible to assess, so most of the following data have been collected retrospectively.
Abnormal cord coiling in its 2 forms, hyper-coiling and non-coiling, have been reported to be more frequent in gestational diabetes118,119 and preeclampsia 119. A higher frequency of thrombosis of chorionic plate vessels, umbilical venous thrombosis, and cord stenosis, has also been reported120.
It is believed that abnormal cord coiling is a chronic state, established in early gestation, that may have chronic (growth retardation) and acute (fetal intolerance to labor and fetal demise) effects on fetal well-being. Yet, the cause of abnormal cord coiling remains unknown in the majority of cases120.
Non-coiled cords and poorly coiled cords
Its frequency is around 4% to 5%121. It has been suggested that these cords are structurally less able to resist external compressive forces. Associations include:
- Intrauterine death.
- Preterm delivery.
- Repetitive intrapartum fetal heart rate decelerations.
- Operative delivery for fetal distress.
- Meconium staining.
- Aneuploidy 103.
Its frequency has been reported as high as 21%120. Associations include:
- Fetal demise123.
- Fetal intrapartum distress.
- Nuchal cord loops124.
Abnormal cord length.
Defined as total length of 40 cm or less125, short umbilical cords are uncommon. This shortness can be real or apparent (due to cord loops or entanglement). These apparent short cords have a greater incidence of forceps deliveries and vacuum extractions than the normal corded fetuses 125. In the other hand, real shortness is found in newborns with early intrauterine constraint126and in those with gross structural or functional limb defects that limit intrauterine movement. It has been associated with:
- Fetal Akinesia Deformation Sequence (FADS) or Pena-Shokeir Sequence, which is a heterogeneous group of disorders in which prolonged decrease or absence of fetal movements results in a series of deformational anomalies: multiple contractures, pulmonary hypoplasia, craniofacial anomalies, polyhydramnios and intrauterine growth retardation127,128. This is an autosomal recessive condition and, therefore, carries a 25% recurrence risk.
- Spinal muscular atrophy (SMA)129.
- Body-stalk anomaly130,131 (also known as short cord umbilical cord syndrome).
- Lateral meningocele syndrome132 (also known as "familial osteosclerosis"133).
- Neu-Laxova syndrome134.
Long umbilical cords, defined as total length over 70 cm, have been significantly associated with135:
- Systemic diseases.
- Delivery complications.
- Increased maternal age.
- Non-reassuring fetal status during labor.
- Respiratory distress.
- Vertex presentation
- Cord entanglement.
- Fetal anomalies.
- Male sex.
- Increased birth weight.
- Increased placental weight.
- Right-twisted cords.
- Hyper-coiled cords.
- True knots.
Abnormal cord width
Thin ("lean") cords
Defined as the cross-sectional area of the cord, measured in a plane adjacent to the insertion into the fetal abdomen, below the 10th centile for gestational age. Lean cords have been associated with136:
- Meconium-stained amniotic fluid at delivery.
- 5-min Apgar score < 7.
- Small for gestational age at birth.
The relation between these and lean cords remain uncertain although some have reported lean umbilical cords differ from normal in some umbilical vein blood flow patterns137.
1.4. Cord bleeding
Most of cases are associated with invasive procedures, such as funipuncture (intended or accidental) or bleeding due to vasa previa after rupture of membranes.
Umbilical ulceration is a rare complication. The only cases reported have been associated with intestinal atresia discovered in the early neonatal period138. No prenatal diagnosis of this anomaly has been done yet.
1.5. Cysts and masses of the cord
Cysts and pseudocysts
Umbilical cord cysts develop from the remnants of the allantois or the omphalo-mesenteric duct. Usually microscopic and with no clinical relevance, they can grow up to several centimeters. They are located mostly on the fetal side and may be detected as early as the first trimester139,140,141.
Pseudocysts are localized edema of Wharton"s jelly, or liquefaction of hematomas or thrombus within the cord, and have the same ultrasound appearance than cysts.
Compared with cysts, pseudocysts have no internal epithelial lining (microscopically). Prenatal ultrasound differential diagnosis is impossible, but also not important since both have been associated with fetal anomalies142. These masses are found in approximately 3% of pregnancies between 7-13 weeks 140. Chromosomal anomalies are found in more than 20% of fetuses with this anomaly, specifically trisomies 18142,143,144 and 13145. Furthermore, it appears to be that cysts and pseudocysts are associated to other structural anomalies in non-chromosomally aberrant fetuses. The natural history of these masses is to resolve by the end of the first trimester. Those that persist beyond 12 weeks and on to the second and third trimester, and the ones near the placental or fetal insertion, are more likely to associate with chromosomal anomalies 144. So, when a cord cyst is encountered, a detailed sonographic survey of the fetus is advisable. Fetal karyotyping is indicated when other anomalies are found or when the cyst persists in to second trimester. If no other anomaly is found, the prognosis is excellent.
The following are examples of first trimester cord cysts.
There is also a short video clip available.
This is another example of persistence of elements found earlier in pregnancy. It is a communication between the dome of the bladder and the umbilicus. In such way, the cord can be dilated distal to the cystic mass due to absorption of fetal urine by Wharton"s jelly146. It has been associated to structural anomalies in up to 46%. These anomalies are:
- Anterior abdominal wall defects,
- Bladder exstrophy and
- Other lesions of the cord :hemangioma, varix, true knot, allantoic or omphalomesenteric cysts.
When no other structural abnormalities are found, the prognosis is excellent and surgery in the neonatal period is advisable147. Many rupture spontaneously.
This image shows the comunication between the umbilicus adn the fetal bladder.
Most cases appear after funipuncture done for diagnostic means. Non-iatrogenic umbilical cord hematoma is very rare. It is associated with non-reassuring patterns of fetal heart rate during labor and with short cords148,149.
Umbilical artery aneurysm is an extremely rare vascular anomaly.
Umbilical artery aneurysm is seen as a cystic lesion with hyperechogenic rim in which color flow and spectral Doppler examinations show nonpulsatile and turbulent blood flow within the artery150,151. It has been reported association with Trisomy 18136, progressive decrease in amniotic fluid volume, and fetal death due to acute umbilical venous compression by the aneurysm150.
Management: delivery as soon as fetal lung maturity is assured when this diagnosis is made prenatally.
Hemangioma of the umbilical cord was first diagnosed prenatally in 1987152. This has been diagnosed as early as 16 weeks153. Hemangioma growth within the cord may impair umbilical circulation and cause fetal demise. Polyhydramnios is also a frequent feature154. It can be misdiagnosed as an omphalocele if its location is near the fetal insertion155. Acute bleeding after spontaneous rupture of the membranes has also been reported156.
Hemangioma nodule and pseudocysts near the placental insertion and gelatin-like swelling adjacent to the nodule.
Few cases reported to date. If three germinal layers are found, and if its position is near the umbilical insertion, consider the differential diagnosis with an acardic amorphus157,158 or a heteropagous conjoined twin. Teratoma should be considered in particular when the lesion contains calcifications.
Rare tumors, that are usually benign but may be associated with fetal death159. They present as solid heterogeneous masses.
The omphalomesenteric duct is the communication between the developing embryonic gut and the yolk sac. The persistence of remnants of the omphalomesenteric duct, within the umbilical cord explains the occasional presence of intestinal tissue. Obliteration of the omphalomesenteric duct is usually complete by the 10th week of gestation. Various portions of the duct may persist, however, giving rise to polyps, fistulas or cysts of the umbilical cord with potentially dangerous clinical consequences, mainly postnatally156,160,161 .The most common of these anomalies is known as Meckel"s diverticulum.
Ectopic liver tissue
Ectopic liver tissue within the cord has been reported postnatally162.
1.6. Cord knots
True cord knots
True knot of the umbilical cord is a common condition rare condition (as high as 1.25%163), which is difficult to diagnose antenatally, even with the use of ultrasound. Up to four true cord knots have been reported164. Constriction of a true knot is however rare but may lead to obstruction of the fetal circulation and subsequent intrauterine death. In fact, fetuses with true umbilical knots are at a four-fold increased risk of intrauterine death165. Yet, large series analyses have shown that the presence of true umbilical cord knots do not alter the incidence of umbilical artery acidemia or change umbilical cord blood gas values. So probably, true umbilical cord knots unless tight have little clinical significance166. It has been reported that true knots are associated with 163,165:
- Advanced maternal age.
- Previous miscarriages.
- Prolonged gravidity.
- Male fetus.
- Long cord.
- Maternal anemia.
- Maternal chronic hypertension.
Pulsed wave Doppler spectral analysis can be used to demonstrate a stenotic effect on the umbilical venous blood flow post-stenotically167. A pre stenotic dilation of the umbilical vein can also be seen.
The following images show a case of true umbilical knot
Ocasionally, a bunch of cord loops make the false impression of a cord knot like in this following case with 3D reconstruction.
There is also a short video clip available.
False cord knots are quite frequent in normal pregnancies and appear due to umbilical artery loops within the cord.
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