Q4: Placenta & Umbilical Cord

What is the approximate weight & shape of the placenta at term?

• 470g

• Round to oval with a 2.2 cm diameter + central thickness of 2.5 cm

From what cells does the placenta differentiate? What is their primary function? What hormone do they secrete?

• Outer trophoblast layer forms the placenta

• Produces multiple hormones and responsible for maternal-fetal gas, nutrients, and waste exchange

• Human chorionic gonadotropin (hCG)

Where do the chorion & chorionic villi arise from? Discuss how the chorion laeve comes about. What is the major functional unit of the placenta. Discuss the fetal & maternal portions of the placenta.

• Chorion = trophoblast // Chorionic villi = chorion

• Chorion laeve = trophoblast layer flattens and loses its villi, forming a smooth membrane

• Placental villi; facilitates nutrient and gas exchange between the mother and fetus

• Fetal portion = formed by chorion frondosum, contains chorionic villi, and connected to fetus via umbilical cord

• Maternal portion = formed by decidua basalis, contains maternal blood in intervillous spaces, and nutrients and oxygen from mother’s blood diffuse through villi to reach fetus

When can the definitive placenta be seen sonographically?

• 12 weeks

Discuss & describe the formation of placental cotyledons

• Aka. chorion villus

• Function = respiration, nutrition, excretion, protection, storage, and hormone production

Discuss through what vessels maternal & fetal blood is brought to the placenta & where gas, nutrient, & waste exchange occur.

• Maternal blood brought to placenta through uterine arteries

• Fetal blood delivered via umbilical arteries

• Occurs within chorion; maternal blood bathes in villi to allow diffusion

What are the functions of the placenta?

• Respiration = oxygen transfer from maternal blood across the placental membrane into fetal blood is by diffusion. Carbon dioxide passes in the opposite direction. The placenta acts as “fetal lungs”

• Nutrition = water, inorganic salts, carbs, fats, proteins, and vitamins pass from maternal blood through the placental membrane into fetal blood

• Excretion = waste products cross membranes from fetal blood and enter maternal blood. Excreted by mother’s kidneys

• Protection = some microorganisms cross the placental border. Storage: carbs, proteins, calcium, and iron are stored in placenta and released into fetal circulation

• Hormonal production = produced by syncytiotrophoblast of placenta; hCG, estrongens, progesterone

What is general rule of how thick the normal placenta should be?  What is the maximum normal thickness of the placenta at term?

• 1.5-2.5 cm; maximum thickness of 4.0 cm

• Abnormal = > 4 cm in the 2nd trimester or 6 cm in the third trimester

• Central thickness = 2.5 cm

List & know at least 8 disorders associated with a thick placenta

• Placentomegaly

• Gestational trophoblastic disease

• Hydrops

• Placental mesenchymal dysplasia

• Chorioangioma

• Neoplasia

• Subchorionic thromboses

• TORCH

List & know at least 6 disorders associated with a thin placenta

• Polyhydramnios

• Small placenta with growth restriction

• Fetal distress

• Preterm labor

• Marginal placenta previa

• Complete placenta previa

What are the factors that increase the significance of a grade 3 placenta?

• Placental calcification; poor uteroplacental blood flow, placental abruption, some adverse neonatal outcomes, and low birth weight

 Placental calcifications are more commonly associated with what factors?

• Advancing gestation

• Increasing maternal serum calcium levels

• Smoking

What conditions are associated with an immature placenta?

• Placental abruption; premature separation of a normally implanted placenta, chronic hypertension, preeclampsia, and preterm rupture of membranes

What placental condition may be associated with an elevated MS-AFP or hCG?

• Chorioangioma

Combined elevation in both AFP & hCG presents a serious risk for what conditions?

• Perinatal mortality & preterm birth

Who is at most risk for developing severe placental insufficiency? What appearance of the placenta & placental cord insertion in the 2^nd trimester may indicate severe placental insufficiency?

• Mothers with diabetes or HTN

• Low diastolic velocity, early diastolic notch, and increases resistance RI >0.58

What are the two main causes for vaginal bleeding in the third trimester?

• Placenta previa

• Placental abruption

 What is the definition of placenta previa? What is its clinical presentation? The diagnosis should not be made prior to how many weeks? Why?

• Condition where the placenta partially or completely covers the cervix; leads to potential bleeding during pregnancy

• Painless vaginal bleeding in the 2nd and 3rd trimesters

• Should not be made prior to 20 weeks due to the possibility of placental migration

What are the risk factors for placenta previa?

• Preterm delivery

• Maternal hemorrhage

• Increased risk of placental invasion

• Increased risk of postpartum hemorrhage

• IUGR

What are the types of placenta previa? What is the criteria for each type?

• Complete or total previa: cervical internal os is completely covered by placental tissue

• Partial previa: partially covers the internal os

• Marginal previa: does not cover the os, but its edge comes to the margin of the os

• Low lying: does not usually have symptoms associated with it

What two conditions may falsely cause the appearance of placenta previa?

• Low-lying placenta covering the internal os secondary to an overdistended bladder

• Uterine focal myometrial contractions

What is placental abruption?  What is it a leading cause of?  If more than 30%-40% of the placenta is affected, what may be the result?

• Separation of normally implanted placenta before term delivery

• Maternal HTN

• Fetal death; without prompt treatment, leads to maternal cardiovascular collapse

What are the clinical presentations of placental abruption?

• Vaginal bleeding

• Abdominal or back pain

• Preterm labor

• Fetal distress or demise

• Uterine irritability

What are the risk factors for placental abruption?

• Hypertension

• Prior abruption

• Short umbilical cord

• Uterine anomaly

• Myomas

• Abdominal trauma

• Placenta previa

• Tobacco use

• Cocaine abuse

What is the sonographic appearance of retroplacental & marginal abruptions?

• Retroplacental abruptions:
  > Thickening of placenta
  > Older hematomas tend to be hypoechoic when compared to the placenta
  > Show separation of placental substance from uterine wall

• Marginal abruption:
  > Subchorionic hemorrhage accumulated at the site of the separation from the placenta

Describe other locations at which placental hemorrhages may occur, their cause, incidence, effect on pregnancy & sonographic appearance

• Retroplacental, subchorionic, subamniotic, and intraplacental sites

• Varies; echogenicity depends on the age of hemorrhage

• Acute bleed = similar echo of placenta

• Subacute and chronic bleed = hypoechoic

Discuss & describe the hypoechoic/cystic lesions such as maternal floor infarction, intervillous thrombosis, perivillous fibrin deposition, decidual cysts, placental lakes, subchorionic fibrin deposition, & subchorionic cysts

• Maternal floor infarction = hypoechoic area in placenta

• Intervillous thrombosis = irregular echogenicity

• Perivillous fibrin deposition and decidual cysts = hypoechoic features, placental lakes are usually echogenic areas

• Subchorionic cysts = identified as cystic structures adjacent to placenta

Discuss & describe the cause, associations, & sonographic appearance of placental infarction

• Usually focal or throughout the placenta; have vascular etiology

• Associated w/ = oligo, umbilical artery doppler abnormalities, IUGR, central nervous system injury, and fetal demise

• Tends to recur in subsequent pregnancies

• Sonographic findings = hyperechoic placental mass or placental thickening

Describe a succenturiate placenta & associated complications

• Accessory lobe(s) = single lobe or multiple lobes to the main placental lobe

• Complication = retained placental accessory lobe after delivery + can lie over the cervix as a variant of placenta previa

Describe circummarginate & circummarginate placenta & discuss associated complications & sonographic appearance

• Circummarginate type = a smooth layer of amniochorionic extends and covers the exposed peripheral placenta

• Circumvallate placenta = amniochorionic folds back onto itself at the perimeter before extending across the outer rim of the placenta; has no distinct sonographic findings

• Sono appearence = thin curvilinear sheet or shelf of tissue bounded on each side by amniotic fluid; sheet or shelf arises from and attached to peripheral margin of placenta

What are uterine synechiae & how can it be distinguished from a circumvallate placenta?

• Uterine synechiae = 1+ linear bands of scar tissue within uterus

• Sono appearance = thick, linear echogenic structure extends from one wall of the uterine cavity across the other and may appear wider at the base; resembles curled peripheral edge of the circumvallate placenta

Discuss & describe the various types of abnormal placental attachment to the uterus including cause, complications, risk factors, sites & sonographic appearance.

• Placenta accreta, increta, and percreta

• Placenta adheres too deeply into the uterine wall or invades surrounding tissues

• Causes = previous uterine surgery or abnormalities

• Complications = hemorrhage and placenta previa

• Risk factors = cesarean delivery history

• Sono appear. = variables in echogenicity and vascularity can indicate abnormal attachment

What is the most common benign placental tumor?  Discuss the types, associated complications & sonographic appearances

• Chorioangioma

• Well-circumscribed solid tumors in the placenta; range from hypoechoic to hyperechoic compared to echogenicity of the placenta

What are the other differentials for solid placental masses?

• Chorioangioma

• Subamniotic hematoma

• Subchorionic hematoma

• Placental hemorrhage

Discuss the umbilical cord including when & from what structures it arises & its structure

• Amniotic membrane covers the umbilical cord

• Umbilical cord = 2 arteries and 1 vein, surrounded by Wharton’s jelly

• Formed by confluence of the chorionic veins of the placenta; oxygenated blood back to the fetus

• Umbilical arteries arise from the internal iliac arteries, alongside the fetal bladder and exit umbilicus to form part of the umbilical cord

What is the most common anomaly of the umbilical cord?  List six abnormalities associated with this anomaly.

• Single umbilical artery

• IUGR (small placenta), increased perinatal mortality, Trisomy 13, 18, 21, Turner’s syndrome, triploidy, and congenital anomalies

What other view may be used as a substitute when an adequate cross-section of the cord cannot be obtained?

• Cord in transverse plane; sees 1 large umbilical vein and 2 smaller umbilical arteries

• View arteries laterally to fetal bladder in a transverse or coronal plane

Describe trophotropism & what effect it can have on the insertion of the umbilical cord into the placenta

• Trophotropism = enlargement of uterus; result in differential growth of the placenta toward the well-vascularized fundus.

• Apparent “migration” of the placenta away from the lower uterine segment with advancing gestational age

Discuss the various types of eccentric cord insertions into the placenta including vasa previa & the associated complications.

• Umbilical cord attaching at edge of the placenta rather than center

• Vasa previa = fetal blood vessels run across the cervical opening

• Complications = vessel rupture and fetal hemorrhage during labor

Discuss the incidence & significance of a nuchal cord

• Umbilical cord wrapped around fetus neck; often in 2nd and 3rd trimesters

• Multiple tight loops indenting the skin in late 3rd trimester

• Nuchal cord = most common cord entanglement in fetus

Discuss significance & risk factors of cord presentation & prolapse

• Cord presentation = position of umbilical cord in relation to presenting part of the fetus during labor

• Risk factors = placenta previa, preterm rupture of membranes, and multiple gestations, leading to potential complications like cord prolapse and fetal distress

 What are the classifications of umbilical cord knots?  What complications are they associated with?

• True knots = twists in the cord; cord compression, reduced blood flow to the fetus, or even stillbirth

• False knots = engorgements of vessels; benign and do not typically cause complications

What are the differentials for umbilical cord cysts? What is their significance?

• Omphalomesenteric cysts: cystic lesion of the umbilical cord caused by persistence and dilatation of a segment of the omphalomesenteric duct lined by epithelium of gastrointestinal origin

• True cysts = epithelium-lined remnants of the allantoic or vitelline ducts and tend to be located closer to the fetal insertion site

• Allantoic cyst = associated with a urachal anomaly

• Single umbilical cord cysts = are identified in approximately 1% of 1st trimester sonograms

• Multiple cysts = increased risk for spontaneous abortion or aneuploidy

Discuss the significance & sonographic appearance of umbilical cord hemangioma, hematoma, varix/aneurysm, & teratoma

• Umbilical cord hemangioma = a benign vascular tumor of the cord, can cause fetal distress through compromised blood flow

• Hematoma = a collection of blood within the cord, leading to potential compression and reduced blood supply to the fetus

• Varix/Aneurysm = abnormal dilation of cord vessels that can pose a risk of rupture and bleeding

• Teratoma = a tumor that can contain multiple tissue types, may affect cord function depending on size and location

List four conditions associated with diffusely enlarged umbilical cords

• Excessive coiling

• True knots

• Multiple loops of nuchal cord

• Cord prolapse