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

2-vessels cords

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:

• stillbirths,
• IUGR,
• 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. 

Single umbilical artery is found in 6,1-11,3% of infants with chromosomal anomalies, mainly trisomies 18 and 13^5,6. 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 encountered^15,16.

Ultrasound appearance
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 Doppler^17,18.

4-vessels cords
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 not^21,22.

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.

Artifacts
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 cases^26,27. 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 fertilization^28,29. 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.

Associated anomalies
Mostly, few anomalies are associated but cases with:

• Aneuploidies⁴⁸.
• Focal liver necrosis39 and calcifications.
• Diaphragmatic hernia⁴⁹.
• Ureteral obstruction⁵⁰.
• Facial anomalies.
• Bell-shaped thorax with increased intermamillary distance.
• Muscular hypotonia.
• Hydrops and cardiovascular anomalies^51,52,53 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 fetuses^58,59).
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 obstructions^{60,61,62,63,64,65,66,67,68,69}.

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 others^72,73,74 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 18^75,76,77,78) has been much less strong then initially though^79,80,81. 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.

Ultrasound appearance
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
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 .
• Polyhydramnios.
• Congenital heart disease.
• Fetal growth restriction.
• Stillbirth.
• Trisomies.

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

Artery
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.

Vein
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 bands^{97, 98, 99, 100}.
• Nuchal loops¹⁰¹.
• True knots ¹⁰¹.
• Fetal grasping^101,102.
• 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

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 fetus^110,111.

Umbilical vein varix

Umbilical vein varix is an uncommon anomaly^17,112,113. 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 diabetes^118,119 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.
• IUGR¹²².

Hyper-coiled cords

Its frequency has been reported as high as 21%¹²⁰. Associations include:

• Fetal demise¹²³.
• Fetal intrapartum distress.
• IUGR.
• Chorioamnionitis.
• Nuchal cord loops¹²⁴.

Abnormal cord length.

Short cords

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 retardation^127,128. This is an autosomal recessive condition and, therefore, carries a 25% recurrence risk.
• Spinal muscular atrophy (SMA)¹²⁹.
• Body-stalk anomaly^130,131 (also known as short cord umbilical cord syndrome).
• Lateral meningocele syndrome¹³² (also known as "familial osteosclerosis"¹³³).
• Neu-Laxova syndrome¹³⁴.

Long cords

Long umbilical cords, defined as total length over 70 cm, have been significantly associated with¹³⁵:

Maternal factors:

• Systemic diseases.
• Delivery complications.
• Increased maternal age.

Fetal factors:

• Non-reassuring fetal status during labor.
• Respiratory distress.
• Vertex presentation
• Cord entanglement.
• Fetal anomalies.
• Male sex.
• Increased birth weight.

Placental features:

• 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.
• Oligohydramnios.
• 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 trimester^139,140,141.

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 18^142,143,144 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.

Patent urachus

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.

Hematoma
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 cords^148,149.

Aneurysm
Umbilical artery aneurysm is an extremely rare vascular anomaly.

Ultrasound appearanceUmbilical 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 artery^150,151. 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
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.

Ultrasound appearance:Hemangioma nodule and pseudocysts near the placental insertion and gelatin-like swelling adjacent to the nodule.

Teratoma
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 amorphus^157,158 or a heteropagous conjoined twin. Teratoma should be considered in particular when the lesion contains calcifications.

Angiomyxoma
Rare tumors, that are usually benign but may be associated with fetal death159. They present as solid heterogeneous masses.

Intestinal polyp

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.
• Multiparity.
• Previous miscarriages.
• Obesity.
• Prolonged gravidity.
• Male fetus.
• Long cord.
• Maternal anemia.
• Maternal chronic hypertension.
• Hydramnios.

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.

1.7. References

1 Fox H. Pathology of the Placenta. London: W.B. Saunders 1978, pp.426-57.

2 Blazer S, Sujov P, Escholi Z, Itai BH, Bronshtein M. Single umbilical artery--right or left? does it matter? Prenat Diagn 1997 Jan;17(1):5-8.

3 Benirschke K, BourneGL. The incidence and prognostic implication of congenital absence of one umbilical artery. Am J Obstet Gynecol 1960; 79: 251-3.

4 Heifetz SA. Single Umbilical Artery. A statistical analyses of 237 autopsy cases and review of the kiterature. Perspect Pediatr Pathol 1984; 8: 345-78.

5 Lilja M. Infants with single umbilical artery studied in a national registry: general epidemiological characteristics. Paediatr Perinat Epidemiol 1991; 5: 27-36.

6 Saller DN Jr, Keen CL, Sun CC, Schwartz S. The association of single umbilical artery with cytogenetically abnormal pregnancies.

7 Clausen I. Umbilical cord anomalies and antenatal fetal demise. Obstet Gynecol Surv.1989; 44: 841-5.

8 Chow JS, Benson CB, Doubilet PM. Frequency and nature of structural anomalies in fetuses with single umbilical arteries. J Ultrasound Med 1998 Dec;17(12):765-8.

9 Thumala MR, Raju TN, Langemberg P. Isolated single artery anomaly and the risk of congenital malformations: a metaanalysis. J Pediatr Surg 1998; 33: 580-5.

10 Weissman A, Drugan A. Sonographic findings of the umbilical cord: implications for the risk of fetal chromosomal anomalies. Ultrasound Obstet Gynecol 2001 Jun;17(6):536-41.

11 Pavlopoulos PM, Konstantinidou AE, Agapitos E, Christodoulou CN, Davaris P. Association of single umbilical artery with congenital malformations of vascular etiology. Pediatr Dev Pathol 1998 Nov-Dec;1(6):487-93.

12 Scalercio F, Ferraro M, Mastrantonio P, Scalercio A. Single umbilical artery (SUA) and congenital eye abnormalities. 2 case reports. Minerva Pediatr 1998 Apr;50(4):141-4.

13 Meizner I, Sherizly I, Mashiach R, Shalev J, Kedron D, Ben-Rafael Z. Prenatal sonographic diagnosis of laryngeal atresia in association with single umbilical artery. J Clin Ultrasound 2000 Oct;28(8):435-8.

14 Petrikovsky B, Schneider E. Prenatal diagnosis and clinical significance of hypoplastic umbilical artery. Prenat Diagn 1996; 16: 93-4.

15 Khong TY, George K. Chromosomal abnormalities associated with a single umbilical artery. Prenat Diagn 1992; 12: 965-8.

16 Rinehart BK, Terrone DA, Taylor CW, Isler CM, Larmon JE, Roberts WE. Single umbilical artery is associated with an increased incidence of structural and chromosomal anomalies and growth restriction. Am J Perinatol 2000;17(5):229-32.

17 Jeanty P. fetal and funicular vascular anomalies: Identification with prenatal ultrasound. Radiology 1989; 173:367-70.

18 Rosenak D, Meizner I. Prenatal sonographic diagnoses of a single and double umbilical artery in the same fetus. J Ultrasound Med 1994; 13: 995-6.

19 Painter D, Russell P. Four-vessel umbilical cord associated with multiple congenital anomalies. Obstet Gynecol 1977 Oct;50(4):505-7

20 Chiappa E, Viora E, Botta G, Abbruzzese PA, Ciriotti G, Campogrande M Arteriovenous fistulas of the placenta in a singleton fetus with large atrial septal defect and anomalous connection of the umbilical veins. Ultrasound Obstet Gynecol 1998 Aug;12(2):132-5

21 Schimmel MS, Eidelman AI Supernumerary umbilical vein resulting in a four-vessel umbilical cord. Am J Perinatol 1998 May;15(5):299-301

22 Rodriguez MA Four-vessel umbilical cord without congenital abnormalities. South Med J 1984 Apr;77(4):539

23 Meyer WW, Lind J, Moinian M An accessory fourth vessel of the umbilical cord. A preliminary study. Am J Obstet Gynecol. 1969 Dec 1;105(7):1063-8

24 Fraser RB, Liston RM, Thompson DL, Wright JR Jr Monoamniotic twins delivered liveborn with a forked umbilical cord. Pediatr Pathol Lab Med 1997 Jul-Aug;17(4):639-44

25 Benirschke K, Kaufmann P: Pathology of the human placenta. New York: Springer-Verlag, 1990 pp. 200-4.

26 Bjoro K: Vascular anomalies of the umbilical cord. II. Perinatal and pediatric implications. Early Hum Dev 8:279-87, 1983.

27 2. Robinson LK, Jones KL, Benirschke K: The nature of structural defects associated with velamentous and marginal insertion of the umbilical cord. Am J Obstet Gynecol 146:191-93, 1983.

28 Oyelese Y, Spong C, Fernandez MA, McLaren RA. Second trimester low-lying placenta and in-vitro fertilization? Exclude vasa previa. J Matern Fetal Med 2000 Nov-Dec;9(6):370-2.

29 Oyelese KO, Turner M, Lees C, Campbell S. Vasa previa: an avoidable obstetric tragedy. Obstet Gynecol Surv 1999 Feb;54(2):138-45.

30 Hata K, Hata T, Fujiwaki R, Ariyuki Y, Manabe A, Kitao M. An accurate antenatal diagnosis of vasa previa with transvaginal color Doppler ultrasonography. Am J Obstet Gynecol 1994 Jul;171(1):265-7.

31 Catanzarite V, Maida C, Thomas W, Mendoza A, Stanco L, Piacquadio KM. Prenatal sonographic diagnosis of vasa previa: ultrasound findings and obstetric outcome in ten cases.Ultrasound Obstet Gynecol. 2001 Aug;18(2):96-9.

32 Lee W, Lee VL, Kirk JS, Sloan CT, Smith RS, Comstock CH. Vasa previa: prenatal diagnosis, natural evolution, and clinical outcome. Obstet Gynecol 2000 Apr;95(4):572-6.

33 Lee W, Kirk JS, Comstock CH, Romero R. Vasa previa: prenatal detection by three-dimensional ultrasonography. Ultrasound Obstet Gynecol 2000 Sep;16(4):384-7.

34 Shin HS, Cho KJ, Suh YL, Chi JG Congenital absence of ductus arteriosus--an autopsy case. J Korean Med Sci 1988 Mar;3(1):41-3

35 Moore L, Toi A, Chitayat D Abnormalities of the intra-abdominal fetal umbilical vein: reports of four cases and a review of the literature. Ultrasound Obstet Gynecol 1996 Jan;7(1):21-5

36 Avni EF, Ghysels M, Donner C, Damis E In utero diagnosis of congenital absence of the ductus venosus. J Clin Ultrasound 1997 Oct;25(8):456-8

37 Yoshinaga K, Kodama K Persistence of the hepatic segment of the left inferior vena cava in man and its relation to the ductus venosus development. Acta Anat (Basel) 1997;160(2):132-8

38 Cohen SB, Lipitz S, Mashiach S, Hegesh J, Achiron R In utero ultrasonographic diagnosis of an aberrant umbilical vein associated with fetal hepatic hyperechogenicity. Prenat Diagn 1997 Oct;17(10):978-82

39 Shryock EH. Janzen J, Barnard MC Report of a newborn human presenting sympus dipus, anomalous umbilical vein, tansposition of the viscera and other anomalies. Anat Rec 82:347, 1942

40 Monie IW: Umbilical vein entering the right atrium: Comments on a previously reported human case. Teratology 4:461, 1971

41 Theander G, Karlsson S. Persistent right umbilical vein. Acta Radiol Diagn (Stockh). 1978;19(1B):268-74.

42 Jouk PS, Champetier J. Abnormal direct entry of the umbilical vein into the right atrium: antenataldetection, embryologic aspects. Surg Radiol Anat. 1991;13(1):59-62.

43 Greiss HB, McGahan JP. Umbilical vein entering the right atrium: significance of in utero diagnosis. J Ultrasound Med. 1992 Mar;11(3):111-3.

44 Tordjeman N, Ville Y, Fermont L, Guis F, Doumerc S, Frydman R. Anomalies of umbilical vein in the fetus. A case report and review of the literature. J Gynecol Obstet Biol Reprod (Paris). 1996;25(5):495-9.

45 Shih JC, Shyu MK, Hsieh MH, Yang JH, Huang SF, Lin GJ, Hsieh FJ. Agenesis of the ductus venosus in a case of monochorionic twins which mimics twin-twin transfusion syndrome. Prenat Diagn. 1996 Mar;16(3):243-6.

46 Fliegel CP, Nars PW. Aberrant umbilical vein. Pediatr Radiol. 1984;14(1):55-6.

47 Currarino G, Stannard MW, Kolni H. Umbilical vein draining into the inferior vena cava via the internal iliac vein, bypassing the liver. Pediatr Radiol. 1991;21(4):265-6.

48 Gembruch U, Baschat AA, Caliebe A, Gortner L Prenatal diagnosis of ductus venosus agenesis: a report of two cases and review of the literature. Ultrasound Obstet Gynecol 1998 Mar;11(3):185-9

49 Strouse PJ, Di Pietro MA, Barr M Jr Pitfall: anomalous umbilical vein and absent ductus venosus in association with right congenital diaphragmatic hernia. Pediatr Radiol 1997 Aug;27(8):651-3

50 Kurimoto S, Kitamura T, Ueki T, Moriyama N, Tajima A Obstruction of the lower ureter caused by an aberrant vessel. Br J Urol 1997 Aug;80(2):355-6

51 Cayol V, Braig S, Noto S, Jannet D, Bouillie J, Marpeau L, Milliez J Agenesia of the canal of Arantius. A case report. J Gynecol Obstet Biol Reprod (Paris) 1997;26(4):430-4

52 Siven M, Ley D, Hagerstrand I, Svenningsen N Agenesis of the ductus venosus and its correlation to hydrops fetalis and the fetal hepatic circulation: case reports and review of the literature. Pediatr Pathol Lab Med 1995 Jan-Feb;15(1):39-50

53 Jorgensen C, Andolf E Four cases of absent ductus venosus: three in combination with severe hydrops fetalis. Fetal Diagn Ther 1994 Nov-Dec;9(6):395-7

54 Leonidas JC, Fellows RA Congenital absence of the ductus venosus: with direct connection between the umbilical vein and the distal inferior vena cava. Am J Roentgenol 1976 Apr;126(4):892-5

55 Laverdiere JT, Laor T, Benacerraf B Congenital absence of the portal vein: case report and MR demonstration. Pediatr Radiol 1995;25(1):52-356 Gembruch U, Baschat AA, Caliebe A, Gortner L Prenatal diagnosis of ductus venosus agenesis: a report of two cases and review of the literature. Ultrasound Obstet Gynecol 1998 Mar;11(3):185-957 Kang YK, Suh YL, Kim CW, Chi JG Fetus in fetu: a case with complete umbilical cord and fetal sac. Pediatr Pathol 1994 May-Jun;14(3):411-958 Sepulveda W, Romero R, Pryde PG, Wolfe HM, Addis JR, Cotton DB. Prenatal diagnosis of sirenomelus with color Doppler ultrasonography. Am J Obstet Gynecol 1994 May;170(5 Pt 1):1377-9

59 Stevenson RE, Jones KL, Phelan MC, Jones MC, Barr M Jr, Clericuzio C, Harley RA, Benirschke K Vascular steal: the pathogenetic mechanism producing sirenomelia and associated defects of the viscera and soft tissues. Pediatrics 1986 Sep;78(3):451-7

60 Ebner I, Dohr G Contribution to the significance of persisting embryonic vessels in the adult organism. Anat Anz 1986;162(2):73-8

61 Miyoshi S, Ikeda M, Kido T, Matsuda Y, Fukada R, Nakajima K, Izukura T Abnormal persistence of the right vitelline vein. J Pediatr Surg 1984 Apr;19(2):204-5

62 Canavese F, Bardini T Intestinal occlusion caused by remnants of the vitelline artery. Pediatr Med Chir 1983 Jul-Aug;5(4):231-2

63 Waldschmidt J Intra-abdominal ligament remnants of the vitelline duct and vessels. Monatsschr Kinderheilkd 1983 Apr;131(4):222-7

64 Raahave D, Bjerre-Jepsen K A vascular band to Meckel"s diverticulum. Ann Chir Gynaecol 1983;72(5):287-8

65 Reichenbach F Chronic duodenal obstruction caused by a persistent vitelline artery. Zentralbl Chir 1982;107(20):1314-6

66 Jankowski A Persistent vitelline artery as cause of ileus in a 12-year-old boy. Wiad Lek 1977 Sep 15;30(18):1465-7

67 Kleinhaus S, Cohen MI, Boley SJ Vitelline artery and vein remnants as a cause of intestinal obstruction. J Pediatr Surg 1974 Jun;9(3):295-9

68 Myers NA, Rubin S Intestinal abstruction due to a persistent vitelline artery. Aust N Z J Surg 1973 Sep;43(2):161-2

69 Prust FW, Abouatme J Vitelline artery causing small bowel obstruction in an adult. Surgery 1969 Apr;65(4):716-20

70 Kokubo T, Okada Y, Itai Y, Iio M Coronary vein flowing into the umbilical portion of the left portal vein: angiographic appearance. Radiat Med 1990 Jul-Aug;8(4):123-4

71 Jeanty P. Persistent right umbilical vein: an ominous prenatal finding? Radiology. 1990 Dec;177(3):735-8.

72 Blazer S, Zimmer EZ, Bronshtein M Persistent intrahepatic right umbilical vein in the fetus: a benign anatomic variant. Obstet Gynecol 2000 Mar;95(3):433-6

73 Miannay E, Dif D, Vaast P, Devisme L, Dufour P, Puech F Persistent right umbilical vein discovered by ultrasonography: prognostic value. Apropos of 2 cases. J Gynecol Obstet Biol Reprod (Paris) 1999 Oct;28(6):563-5

74 Wolman I, Gull I, Fait G, Amster R, Kupferminc MJ, Lessing JB, Jaffa AJ. Persistent right umbilical vein: incidence and significance.Ultrasound Obstet Gynecol 2002 Jun;19(6):562-4.

75 Bell AD, Gerlis LM, Variend S. Persistent right umbilical vein--case report and review of literature. Int J Cardiol. 1986 Feb;10(2):167-76.

76 De Catte L, Osmanagaoglu K, De Schrijver I Persistent right umbilical vein in trisomy 18: sonographic observation. J Ultrasound Med 1998 Dec;17(12):775-9

77 Ami MB, Perlitz Y, Matilsky M Prenatal sonographic diagnosis of persistent right umbilical vein with varix. J Clin Ultrasound 1999 Jun;27(5):273-5

78 Lai WW Prenatal diagnosis of abnormal persistence of the right or left umbilical vein: report of 4 cases and literature review. J Am Soc Echocardiogr 1998 Sep;11(9):905-9

79 Kirsch CF, Feldstein VA, Goldstein RB, Filly RA. Persistent intrahepatic right umbilical vein: a prenatal sonographic series without significant anomalies. J Ultrasound Med. 1996 May;15(5):371-4.

80 Blazer S, Zimmer EZ, Bronshtein M. Persistent intrahepatic right umbilical vein in the fetus: a benign anatomic variant. Obstet Gynecol 2000 Mar;95(3):433-6.

81 Shen O, Tadmor OP, Yagel S. Prenatal diagnosis of persistent right umbilical vein. Ultrasound Obstet Gynecol 1996 Jul;8(1):31-3.

82 Ami MB, Perlitz Y, Matilsky M. Prenatal sonographic diagnosis of persistent right umbilical vein with varix. J Clin Ultrasound 1999 Jun;27(5):273-5.

83 Hager J, Gschnitzer F, Hammerer I, Gassner I. Congenital epigastric-umbilical arteriovenous fistula. Contribution on a rare clinical picture. Langenbecks Arch Chir 1982;357(4):269-73.

84 Dolkart LA, Reimers FT, Kuonen CA Discordant umbilical arteries: ultrasonographic and Doppler analysis. Obstet Gynecol 1992 Jan;79(1):59-63

85 Petrikovsky B, Schneider E Prenatal diagnosis and clinical significance of hypoplastic umbilical artery. Prenat Diagn 1996 Oct;16(10):938-40

86 Raio L, Ghezzi F, Di Naro E, Gomez R, Saile G, Bruhwiler H The clinical significance of antenatal detection of discordant umbilical arteries. Obstet Gynecol 1998 Jan;91(1):86-91

87 Meir K, Yagel S, Amsalem H, Ariel I. Single umbilical artery stenosis associated with intrauterine fetal death post-transfusion. Prenat Diagn 2002 Mar;22(3):186-8.

88 Smith JF Jr, Warner KD, Bergmann M, Pushchak MJ. Umbilical artery regression: a rare complication of intravascular fetal transfusion. Obstet Gynecol 1999 May;93(5 Pt 2):828-9.

89 Malee MP, Carr S, Rubin LP, Johal J, Feit L Prenatal ultrasound diagnosis of abdominal aortic aneurysm with fibrotic occlusion in aortic branch vessels. Prenat Diagn 1997 May;17(5):479-82

90 Wolf HK, MacDonald J, Bradford WB, Lanman JT Jr Acardius anceps with evidence of intrauterine vascular occlusion: report of a case and discussion of the pathogenesis. Pediatr Pathol 1991 Jan-Feb;11(1):143-52

91 Cook V, Weeks J, Brown J, Bendon R Umbilical artery occlusion and fetoplacental thromboembolism. Obstet Gynecol 1995 May;85(5 Pt 2):870-2

92 Baxi LV, Daftary A, Loucopoulos A Single fetal demise in a twin gestation: umbilical vein thrombosis. Gynecol Obstet Invest 1998;46(4):266-7

93 Baxi LV, Daftary A, Loucopoulos A. Single fetal demise in a twin gestation: umbilical vein thrombosis. Gynecol Obstet Invest 1998;46(4):266-7.

94 Fritz MA, Christopher CR. Umbilical vein thrombosis and maternal diabetes mellitus. J Reprod Med 1981 Jun;26(6):320-4.

95 Qureshi F, Jacques SM Marked segmental thinning of the umbilical cord vessels. Arch Pathol Lab Med 1994 Aug;118(8):826-30

96 Hallak M, Pryde PG, Qureshi F, Johnson MP, Jacques SM, Evans MI. Constriction of the umbilical cord leading to fetal death. A report of three cases. J Reprod Med 1994 Jul;39(7):561-5.

97 Kanayama MD, Gaffey TA, Ogburn PL Jr. Constriction of the umbilical cord by an amniotic band, with fetal compromise illustrated by reverse diastolic flow in the umbilical artery. A case report. J Reprod Med 1995 Jan;40(1):71-3.

98 Boughizane S, Zhioua F, Jedoui A, Kattech R, Gargoubi N, Srasra M, Ben Romdhane K, Meriah S. Swallowing of an amniotic string by a fetus at term. J Gynecol Obstet Biol Reprod (Paris) 1993;22(4):409-10.

99 Heifetz SA. Strangulation of the umbilical cord by amniotic bands: report of 6 cases and literature review. Pediatr Pathol 1984;2(3):285-304.

100 Reles A, Friedmann W, Vogel M, Dudenhausen JW. Intrauterine fetal death after strangulation of the umbilical cord by amniotic bands. Geburtshilfe Frauenheilkd 1991 Dec;51(12):1006-8.

101 Sherer DM, Anyaegbunam A. Prenatal ultrasonographic morphologic assessment of the umbilical cord: a review. Part I. Obstet Gynecol Surv 1997 Aug;52(8):506-14.

102 Heyl W, Rath W. Intrapartum therapy-resistant fetal bradycardia--color Doppler sonographic diagnosis of umbilical cord compression due to fetal grasping. Z Geburtshilfe Neonatol 1996 Jan-Feb;200(1):30-2.

103 Ertan AK, Schmidt W. Umbilical cord entanglement and color-coded Doppler ultrasound. Geburtshilfe Frauenheilkd 1994 Apr;54(4):196-203.

104 Larson JD, Rayburn WF, Harlan VL. Nuchal cord entanglement and gestational age . Am J Perinatol 1997; 14(9): 555-557.

105 Adinma JI. Effect of cord entanglement on pregnancy outcome. Int J Gynaecol Obstet 1990 May;32(1):15-8.

106 Lipitz S, Seidman DS, Gale R, Stevenson DK, Alcalay M, Menczer J, Barkai G. Is fetal growth affected by cord entanglement? J Perinatol 1993 Sep-Oct;13(5):385-8.

107 Giacomello F. Ultrasound determination of nuchal cord breech presentation. Am J Obstet Gynecol 1988; 159: 531-2.

108 Corridan M, Kendall ED, Begg JD. Cord entanglement causing premature placental separation and amniotic fluid embolism. Case report. Br J Obstet Gynaecol 1980 Nov;87(11):935-40.

109 Muth H, Engelbrecht R. Acute occlusion of the arterial blood supply of the right arm in a newborn following entanglement of the umbilical cord. Geburtshilfe Frauenheilkd 1976 Dec;36(12):1099-101.

110 Shahabi S, Donner C, Wallond J, Schlikker I, Avni EF, Rodesch F. Monoamniotic twin cord entanglement. A case report with color flow Doppler Ultrasonography for antenatal diagnosis. J Reprod Med 1997 Nov;42(11):740-2.

111 Westover T, Guzman ER, Shen-Schwarz S. Prenatal diagnosis of an unusual nuchal cord complication in monoamniotic twins. Obstet Gynecol 1994 Oct;84(4 Pt 2):689-91.

112 Prefumo F, Thilaganathan B, Tekay A. Antenatal diagnosis of fetal intra-abdominal umbilical vein dilatation.Ultrasound Obstet Gynecol 2001 Jan;17(1):82-5

113 Zalel Y, Lehavi O, Heifetz S, Aizenstein O, Dolitzki M, Lipitz S, Achiron R. Varix of the fetal intra-abdominal umbilical vein: prenatal sonographic diagnosis and suggested in utero management. Ultrasound Obstet Gynecol 2000 Oct;16(5):476-8.

114 Batton DG, Amanullah A, Comstock C. Fetal schistocytic hemolytic anemia and umbilical vein varix. J Pediatr Hematol Oncol 2000 May-Jun;22(3):259-61.

115 Sepulveda W, Mackenna A, Sanchez J, Corral E, Carstens E. Fetal prognosis in varix of the intrafetal umbilical vein. J Ultrasound Med 1998 Mar;17(3):171-5.

116 Schrocksnadel H, Holbock E, Mitterschiffthaler G, Totsch M, Dapunt O. Thrombotic occlusion of an umbilical vein varix causing fetal death. Arch Gynecol Obstet 1991;248(4):213-5.

117 Strong TH Jr, Jarles DL, Vega JS, Feldman DB. Am J Obstet Gynecol. The umbilical coiling index. 1995 Feb;172(2 Pt 1):718-20.

118 Ezimokhai M, Rizk DE, Thomas L. Abnormal vascular coiling of the umbilical cord in gestational diabetes mellitus. Arch Physiol Biochem 2001 Jul;109(3):209-14.

119 Ezimokhai M, Rizk DE, Thomas L. Maternal risk factors for abnormal vascular coiling of the umbilical cord. Am J Perinatol 2000;17(8):441-5.

120 Machin GA, Ackerman J, Gilbert-Barness E. Abnormal umbilical cord coiling is associated with adverse perinatal outcomes. Pediatr Dev Pathol 2000 Sep-Oct;3(5):462-71.

121 Strong TH Jr, Elliott JP, Radin TG. Non-coiled umbilical blood vessels: a new marker for the fetus at risk. Obstet Gynecol 1993 Mar;81(3):409-11.

122 Degani S, Leibovich Z, Shapiro I, Gonen R, Ohel G. Early second-trimester low umbilical coiling index predicts small-for-gestational-age fetuses. J Ultrasound Med 2001 Nov;20(11):1183-8.

123 Herman A, Zabow P, Segal M, Ron-el R, Bukovsky Y, Caspi E. Extremely large number of twists of the umbilical cord causing torsion and intrauterine fetal death. Int J Gynaecol Obstet 1991 Jun;35(2):165-7.

124 Strong TH Jr, Manriquez-Gilpin MP, Gilpin BG. Umbilical vascular coiling and nuchal entanglement. J Matern Fetal Med 1996 Nov-Dec;5(6):359-61.

125 Sornes T. Short umbilical cord as a cause of fetal distress. Acta Obstet Gynecol Scand 1989;68(7):609-11.

126 Miller ME, Higginbottom M, Smith DW. Short umbilical cord: its origin and relevance. Pediatrics 1981 May;67(5):618-21.

127 Ho NC. Monozygotic twins with fetal akinesia: the importance of clinicopathological work-up in predicting risks of recurrence. Neuropediatrics 2000 Oct;31(5):252-6.

128 Hall JG. Analysis of Pena Shokeir phenotype. Am J Med Genet 1986 Sep;25(1):99-117.

129 Gonzalez De Dios J, Martinez Frias ML, Arroyo Carrera I, Fondevilla Sauci J, Sanchis Calvo A, Hernandez Ramon F, Martinez Guardia N, Garcia Gonzalez MM. Role of signs of fetal hypokinesia in the diagnosis of spinal muscular atrophy of neonatal onset. An Esp Pediatr 2002 Mar;56(3):233-40.

130 Daskalakis GJ, Nicolaides KH. Monozygotic twins discordant for body stalk anomaly. Ultrasound Obstet Gynecol 2002 Jul;20(1):79-81.

131 Negishi H, Yaegashi M, Kato EH, Yamada H, Okuyama K, Fujimoto S. Prenatal diagnosis of limb-body wall complex. J Reprod Med 1998 Aug;43(8):659-64.

132 Gripp KW, Scott CI Jr, Hughes HE, Wallerstein R, Nicholson L, States L, Bason LD, Kaplan P, Zderic SA, Duhaime AC, Miller F, Magnusson MR, Zackai EH. Lateral meningocele syndrome: three new patients and review of the literature. Am J Med Genet 1997 Jun 13;70(3):229-39

133 Philip et al. Familial osteosclerosis. J Pediatr 1977 90:49-54.134 King JA, Gardner V, Chen H, Blackburn W. Neu-Laxova syndrome: pathological evaluation of a fetus and review of the literature.Pediatr Pathol Lab Med 1995 Jan-Feb;15(1):57-79.

135 Baergen RN, Malicki D, Behling C, Benirschke K. Morbidity, mortality, and placental pathology in excessively long umbilical cords: retrospective study. Pediatr Dev Pathol 2001 Mar-Apr;4(2):144-53.

136 Raio L, Ghezzi F, Di Naro E, Franchi M, Maymon E, Mueller MD, Bruhwiler H. Prenatal diagnosis of a lean umbilical cord: a simple marker for the fetus at risk of being small for gestational age at birth. Ultrasound Obstet Gynecol. 1999 Mar;13(3):157-60.

137 Di Naro E, Ghezzi F, Raio L, Franchi M, D"Addario V, Lanzillotti G, Schneider H. Umbilical vein blood flow in fetuses with normal and lean umbilical cord. Ultrasound Obstet Gynecol 2001 Mar;17(3):224-8.

138 Yamanaka M, Ohyama M, Koresawa M, Kawataki M, Ohsaki I, Tanaka Y. Umbilical cord ulceration and intestinal atresia. Eur J Obstet Gynecol Reprod Biol 1996 Dec 27;70(2):209-12.

139 Skibo LK, Lyons EA, Levi CS. First-trimester umbilical cord cysts. Radiology 1992; 182:719-22.

140 Ross JA, Jurcovic D, Zosmer N, Jauniaux E, Hacket E, Nicolaides KH. Umbilical cord cysts early in pregnancy. Obstet Gynecol 1997; 89:442-5.

141 Sepulveda W, Leible S, Ulloa A, Ivankovic M, Schnapp C. Clinical significance of first trimester umbilical cord cysts. J Ultrasound Med 1999; 18: 95-9.

142 Jauniaux E, Donner C, Thomas C, Francotte J, Rodesch F, Avni FE. Umbilical cord pseudocyst in trisomy18. Prenat Diagn 1988; 8:557-63.

143 Ramirez P, Haberman S, Baxi L. Significance of prenatal diagnosis of umbilical cord cyst in a afetus with trisomy 18. Am J Obstet Gynecol 1995; 173: 955-7.

144 Sepulveda W, Gutierrez J, Sanchez J, Be C, Schnapp C. Pseudocyst of the umbilical cord: prenatal sonographic appearance and clinical significance. Obstet Gynecol 1999; 93: 377-81.

145 Zelante L, Dallapiccola B. Umbilical cord pseudocyst in trisomy 13. Prenat Diagn 1989; 9:448-9.

146 4. Tsuchida Y, Ishida M. Osmolar relationship between enlarged umbilical cord and patent urachus. J Pediatr Surg 4:465- 67, 1969.

147 6. Rich RH, Hardy BE, Filler RM. Surgery for anomalies of the urachus. J Pediatr Surg 18:370-372, 1983.

148 Seoud M, Aboul-Hosn L, Nassar A, Khalil A, Usta I. Spontaneous umbilical cord hematoma: a rare cause of acute fetal distress. Am J Perinatol 2001;18(2):99-10.

149 Csecsei K, Kovacs T. Spontaneous haematoma of the umbilical cord with a single umbilical artery. Eur J Obstet Gynecol Reprod Biol 1996 Feb;64(2):231-3

150 Berg C, Geipel A, Germer U, Gloeckner-Hofmann K, Gembruch U. Prenatal diagnosis of umbilical cord aneurysm in a fetus with trisomy 18. Ultrasound Obstet Gynecol 2001 Jan;17(1):79-81.

151 Siddiqi TA, Bendon R, Schultz DM, Miodovnik M. Umbilical artery aneurysm: prenatal diagnosis and management. Obstet Gynecol 1992 Sep;80(3 Pt 2):530-3.

152 Mishriki YY, Vanyshelbaum Y, Epstein H, Blanc W. Hemangioma of the umbilical cord. Pediatr Pathol 1987;7(1):43-9.

153 Kamitomo M, Sueyoshi K, Matsukita S, Matsuda Y, Hatae M, Ikenoue T. Hemangioma of the umbilical cord: stenotic change of the umbilical vessels. Fetal Diagn Ther 1999 Nov-Dec;14(6):328-31.

154 Armes JE, Billson VR. Umbilical cord hemangioma associated with polyhydramnios, congenital abnormalities and perinatal death in a twin pregnancy. Pathology 1994 Apr;26(2):218-20.

155 Miller KA, Gauderer MW. Hemangioma of the umbilical cord mimicking an omphalocele. J Pediatr Surg 1997 Jun;32(6):810-2.

156 Dombrowski MP, Budev H, Wolfe HM, Sokol RJ, Perrin E. Fetal hemorrhage from umbilical cord hemangioma. Obstet Gynecol 1987 Sep;70(3 Pt 2):439-42.

157 Kreczy A, Alge A, Menardi G, Gassner I, Gschwendtner A, Mikuz G. Teratoma of the umbilical cord. Case report with review of the literature. Arch Pathol Lab Med 1994 Sep;118(9):934-7.

158 Wagner H, Baretton G, Wisser J, Babic R, Lohrs U. Teratoma of the umbilical cord. Case report with literature review. Pathologe 1993 Dec;14(6):395-8.

159 Fortune DW, Ostor AG. Angiomyxomas of the umbilical cord. Obstet Gynecol 1980 Mar;55(3):375-8.

160 Guschmann M, Janda J, Wenzelides K, Vogel M. Intestinal polyp of the umbilical cord. Zentralbl Gynakol 2002 Feb;124(2):132-4.

161 Iwasaki I, Yu TJ, Itahashi K, Nito A, Yamaguchi H, Onoki J. Isolated well-formed intestinal tissue in the umbilical cord. A variant of cyst of omphalomesenteric duct. Acta Pathol Jpn 1986 Apr;36(4):565-9.

162 Preminger A, Udassin R, Pappo O, Arad I. Ectopic liver tissue within the umbilical cord. J Pediatr Surg 2001 Jul;36(7):1085-6.

163 Airas U, Heinonen S. Clinical significance of true umbilical knots: a population-based analysis. Am J Perinatol 2002 Apr;19(3):127-32.

164 Jones I. A truly knotted cord. Aust N Z J Obstet Gynaecol 1998 Feb;38(1):98-9.

165 Hershkovitz R, Silberstein T, Sheiner E, Shoham-Vardi I, Holcberg G, Katz M, Mazor M. Risk factors associated with true knots of the umbilical cord. Eur J Obstet Gynecol Reprod Biol 2001 Sep;98(1):36-9.

166 Maher JT, Conti JA. A comparison of umbilical cord blood gas values between newborns with and without true knots. Obstet Gynecol 1996 Nov;88(5):863-6.

167 Gembruch U, Baschat AA. True knot of the umbilical cord: transient constrictive effect to umbilical venous blood flow demonstrated by Doppler sonography. Ultrasound Obstet Gynecol 1996 Jul;8(1):53-6.