STUDY GUIDE UMBILICAL CORD & AMNIOTIC FLUID

What are the components of the umbilical cord?

The umbilical cord consists of 2 arteries and 1 vein.

What are the two shapes of umbilical cord?

it may be spiraled or helical

All aspects of umbilical cord development are complete by ________ gestation

• 4 to 5 weeks

• 15 to 20 weeks

• 10 to 11 weeks

• 8 to 9 weeks

10 to 11 weeks

True/False: The normal umbilical cord is shown with its placental insertion site and is covered by a glistening layer of amnion

true

What is the average length of a normal umbilical cord?

The average length of a normal umbilical cord is 51-61 cm.

True/False: In the umbilical cord, veins are longer than arteries

false, because arteries are longer than vein

What does the single umbilical vein do?

carries oxygenated blood into ductus venosus to be sent to IVC, then heart for recirculation

What do the two umbilical arteries do?

carry deoxygenated blood back to placenta for oxygen exchange

The umbilical arteries are branches of the fetal internal iliac arteries and bring deoxygenated blood from the fetus to the placenta. Where does each artery course and enter?

Each artery courses around the fetal bladder and enters the umbilical cord at the abdominal CI (cord insertion site).

Where does the umbilical vein course and enter?

The umbilical vein brings oxygenated blood from the placenta to the fetus and enters the fetal liver at the abdominal cord insertion site.

What is the fate of a significant portion of umbilical venous blood?

About 50% of umbilical venous blood is shunted through the ductus venosus to the inferior vena cava before entering the right atrium

What is normal arterial flow in the umbilical cord?

low resistance with good diastolic flow

Increased resistance will cause what?

decreased diastolic flow which indicates increased resistance to flow in the fetus

How do umbilical arteries function in fetal circulation?

The two umbilical arteries carry deoxygenated blood from the fetus back to the placenta for oxygen exchange.

What is Wharton's jelly?

a protective substance that surrounds the vessels within the umbilical cord

What are the 3 areas to assess when it comes to umbilical cord?

o Placental attachment
o Free loop
o Entry into the abdomen

When does a nuchal cord occur?

A nuchal cord occurs when the umbilical cord becomes entangled at 360 degrees around the fetal neck

The prevalence of nuchal cords at birth is around ______ of all pregnancies with no significant statistical association between the presence of a nuchal cord and stillbirth

• 44%

• 10%

• 75%

• 22%

22%

On the other hand, multiple loops of nuchal cord have been associated with what?

abnormal fetal heart rate pattern during labor, low umbilical artery pH, an increased likelihood of Cesarean section or operative deliveries and an Apgar score < 7 at the 5th minute

What are tight nuchal loops associated and not associated with?

they are associated with a low Apgar score but not with an increased admission to the neonatal intensive care unit (NICU)

What are loose loops of nuchal cord associated with?

They are associated with a favorable in utero prognosis and perinatal outcome.

What is vasa previa?

a rare obstetrical pathology that affects 0.046% of all pregnancies, in which the fetal blood vessels are located within the membranes, not in their usual location protected by the umbilical cord
or the placenta, and cover the internal cervical os

What are the 3 types of vasa previa?

i. Type I, when there is one single placental lobe with a velamentous cord
ii. Type II, when the unprotected fetal vessels connect two lobes of a succenturiate lobed or bilobed placenta, near the cervix
iii. Type III, when the fetal vessel runs within the membranes, near the cervix, but is not associated with a velamentous cord insertion or bilobed placenta

Vasa previa has a resolution rate varying from 14% to 39% up to 28 weeks of gestational age, especially if diagnosed before ________ of gestation, if not covering the internal cervical os and when not associated with placenta previa

24 weeks

With vasa previa, what are the gold standard diagnostic modalities however, due to the low incidence of this condition, there are no population screening protocols, and the screening approach is indicated only in high-risk patients, such as low-lying placenta/placenta previa, velamentous cord insertion, ART and multiple gestations

transvaginal ultrasound and color Doppler ultrasound

Elective Cesarean section should be planned around how many weeks?

around 35 weeks and not after 37 week’s gestation

What is velamentous umbilical cord insertion?

one of the abnormal cord insertion types, in which the vessels run through the amnion and chorion, unprotected by Wharton’s jelly, before reaching the placental plate (This abnormality is present in 1.5% of singleton pregnancies)

What are the risk factors associated with velamentous umbilical cord insertion?

bilobate/succenturiate placenta, ART, multiple gestation and a prior history of abnormal placental cord insertion

What type of cord insertion describes the following?

a. is another anomaly, in which the umbilical cord is inserted into the placental margin within 2.0 cm
b. It is present in 6.3% of singleton pregnancies and presents much lower chances of complications than velamentous cord insertion

Marginal umbilical cord insertion

What cord insertion describes the following?

a. is a condition where the umbilical vessels separate before they insert into the placental plate and lose their Wharton’s jelly
b. It is present in 0.1% of pregnancies and is considered a variant not well distinguished from velamentous cord insertion

Furcate umbilical cord insertion

What cord insertion does the following describe?

a. a condition exclusively of monoamniotic twin pregnancies, occurs because both umbilical cords insert close to each other in single placenta
b. entangled cords can cause vascular damage for one or both fetuses and lead to fetal demise
c. Diagnosis can be made through the visualization of a branch pattern on color Doppler ultrasound at the level of the entanglement, and an end systolic notch seen on the umbilical artery waveform reflects vascular compression or narrowing

Umbilical cord entanglement

What does the following describe?

b. Allantoic: persistent urachus forms cystic structure within cord
c. Omphalomesenteric: persistent omphalomesenteric duct form cystic structure within cord
d. Usually causes no related complications if blood flow unaffected
e. Umbilical cord cysts can be classified as true cysts and pseudocysts.
f. They are usually located close to fetal cord insertion and vary between 4–6 mm in diameter.

Umbilical Cord Cyst

True/False: True cysts are present in 3.4% of first trimester pregnancies and 20% of those persist into the second trimester

true

What pathology does the following describe?

a. are more frequent than true cysts and tend to be located close to the fetal heart insertion site of the umbilical cord
b. They are formed by localized edema and the liquefaction of the Wharton’s jelly and have no epithelial lining
c. These cysts are associated with fetal trisomy and other congenital anomalies, including exomphalos, vertebral defects, imperforate anus, and tracheoesophageal fistula

Pseudocysts (Wharton’s jelly cysts)

If another fetal anomaly is seen together with umbilical cord cyst, what is indicated?

karyotyping

How prevalent is a single umbilical artery (SUA) in pregnancies?

A single umbilical artery is present in 1.0% of all pregnancies (with greater frequency of an absent left umbilical artery than absent right umbilical artery).

What does the following describe?

- Single umbilical artery present within the cord
- Most common cord abnormality
- Can present as a solitary abnormality
- Can be associated with:
i. GU anomalies
ii. CNS anomalies
iii. Omphalocele
iv. Cardiac anomalies
v. Trisomy 13 and 18

single umbilical artery (SUA)

What condition does the following describe?

a. is a rare condition in which there is a focal
dilatation larger than 9.0 mm in the intrahepatic or extrahepatic portion of the umbilical vein
b. It is associated with a 5.8% risk of chromosomal aneuploidy, especially trisomy 21, and a 19% risk of additional ultrasound anomalies
c. At ultrasound examination, a cystic structure is seen in the fetal abdomen, showing differential diagnosis to normal fetal gallbladder and fetal stomach mesenteric or omental cysts and umbilical artery aneurysms
d. Doppler ultrasound evaluation is essential for a correct diagnosis

Umbilical cord varix

Risk factors for umbilical vessel thrombosis include what?

the hyper coiling of the umbilical cord and deficient Wharton’s jelly

What is a rare event and is associated with
intrauterine growth restriction, fetal organ infarcts and stillbirth?

Umbilical artery thrombosis

What is also a rare event and is associated with worse perinatal outcomes when compared to umbilical artery thrombosis, as there is only one vein in the umbilical cord to deliver oxygenated blood from the mother to the fetus?

Umbilical vein thrombosis

What pathology does the following describe?

a. is the most common tumor of the umbilical cord, although it is exceedingly rare.
b. These masses, unlike allantoic cysts, appear as solid hyperechoic masses and are more often located near the cord insertion site into the placenta.

Umbilical cord hemangioma

What do we know about amniotic fluid in the 1st trimester?

o Production poorly understood
o Multiple sources (maternal: placenta and membranes)

What is a major contributor from 16 weeks onwards?

Fetal urine (and lungs)

Assessment of AFV is assessment of…..

fetal well being

What are the abnormal amniotic fluid volumes?

o Increased – polyhydramnios
o Decreased – oligohydramnios
o No fluid – anhydramnios

Echogenic debris in the amniotic fluid may be what?

vernix or meconium (with meconium being the least likely to be observed during an otherwise normal examination)

What are the several important functions of amniotic fluid?

o protecting the fetus from trauma
o temperature regulation
o musculoskeletal maturity
o normal lung
o gastrointestinal development

True/False: In the second half of the pregnancy, the fetal kidneys and lungs produce most of the amniotic fluid, with urine being the greatest contributor

true

What are the 3 methods of assessment for amniotic fluid?

o SUBJECTIVE
o SINGLE DEEPEST VERTICAL POOL

o AFI - AMNIOTIC FLUID INDEX

Describe the method of single deepest vertical pool?

The maximum vertical pocket, also referred to as the deepest vertical pocket, may be used. This pocket should contain no fetal parts or umbilical cord and measure at least 2 cm, with a normal range between 2 and 8 cm.

Describe the method of amniotic fluid index (AFI)?

The most widely accepted means of evaluating the volume of amniotic fluid is the amniotic fluid index (AFI). The AFI is measured using the anteroposterior dimensions obtained from the four quadrants of the amniotic sac and adding them together. Once more, these measurements should not include fetal parts or umbilical cord. Color Doppler can be used to ensure that no cord is included. For the measurement, the transducer must be placed perpendicular to the floor. The “normal” amount of fluid varies with gestation. Normal is 5-24 cm.

What does oligohydramnios refer to?

refers to a decreased amount of amniotic fluid

What are some complications associated with polyhydramnios?

Complications of polyhydramnios include cardiac/chest abnormalities, chromosomal abnormalities, and esophageal atresia.

What is the measurement for polyhydramnios?

• DVP - greater than or equal to 8 cm

• AFI - greater than or equal to 24cm

What is the measurement for oligohydramnios?

• DVP: < 2cm

• AFI: < 5cm

When an abnormality is noted in the amount of amniotic fluid, a thorough evaluation of the fetal __________ for abnormalities should be conducted, although other systems may be the reason for the imbalance

genitourinary system and gastrointestinal system

Amniotic fluid is also constantly being swallowed by the developing fetus and absorbed by the gastrointestinal tract. Therefore, when polyhydramnios is present _______should be primarily suspected.

abnormalities of the fetal gastrointestinal system

 What abnormalities should be suspected when oligohydramnios is observed?

abnormalities of the urinary system should be initially suspected

Fetal malformations and complications associated with polyhydramnios

✓ Cardiac and/or chest abnormalities
✓ Chromosomal abnormalities
✓ Duodenal atresia
✓ Esophageal atresia
✓ Gastroschisis
✓ Neural tube defects
✓ Omphalocele
✓ Rh incompatibility
✓ Twin–twin transfusion syndrome

Fetal malformation and complications
associated with oligohydramnios

✓ Bilateral multicyclic dysplastic kidney disease
✓ Bilateral renal agenesis
✓ Infantile polycystic kidney disease
✓ Intrauterine growth restriction
✓ Posterior urethral valves
✓ Premature rupture of membranes (PROM)