Placenta and Umbilical Cord Abnormalities - Comprehensive Study Notes

Placental Thickness Abnormalities

• Placental thickness normally < $5\ \text{cm}$ AP.

• Increased placental thickness: > $5\ \text{cm}$ associated with:

  • Gestational diabetes mellitus

  • Rh isoimmunization

  • Maternal infection

  • Chorioangioma

  • Multiple gestation

  • Maternal anemia

  • Hydrops fetalis

  • Sacrococcygeal teratoma

  • Partial mole

  • Chromosome abnormalities

  • Abruption (appears thick due to retroplacental clot)

• Decreased placental thickness (< $1.5\ \text{cm}$):

  • Pre-eclampsia

  • IUGR

  • Diabetes mellitus predating pregnancy

  • Intrauterine infection

  • ? Polyhydramnios (appears thinner)

Placental Variants

Extrachorial Types

• Placenta in which the membranous chorion does not extend to the edge.

• Almost 20% of delivered placentas show partial extrachorial regions.

• Types:

  • Circumvallate placenta: small central chorionic ring surrounded by thickened amnion and chorion. May predispose to early separation, antepartum bleeding, and threatened abortion.

  • Circummarginate placenta: central attachment of membranes without a central ring.

Accessory Types (due to alterations in mechanics of early placentation)

• Succenturiate: an accessory cotyledon with vascular connections to the main placenta.

• Bipartite: placenta divided into two lobes but united by primary vessels and membranes.

• Annular: a ring-shaped placenta.

Placenta Previa

• Definition: placental tissue encroaching upon the cervix and/or crossing the internal cervical os.

• Cause: abnormally low implantation of the blastocyst.

• Risk factors: multiparity; prior C-section or myomectomy; multiple abortions with instrumentation causing uterine scarring.

• Classic symptom: painless vaginal bleeding in the 3rd trimester.

• Best diagnosed sonographically in the 3rd trimester due to placental migration.

• Scanning pitfall: overdistended maternal bladder or focal myometrial contraction can yield a false positive.

Classification of placenta previa

• Complete/total/central previa: placenta completely covering the internal os.

• Incomplete placenta previa: placenta partially covering the internal os, including marginal coverage.

• Low Lying Placenta (not a type of previa): placenta is within $2\ \text{cm}$ of the internal os in the lower uterine segment.

Placental Abruption / Abruptio Placenta

• Premature separation of all or part of a normally implanted placenta from the myometrium.

• Predisposing factors:

  • Maternal hypertension

  • Advanced maternal age

  • Multiparity

  • Maternal vascular disease

  • Cigarette smoking

  • Trauma

  • Cocaine use

  • Uterine leiomyomas

• Symptoms: abdominal pain; may or may not have vaginal bleeding (depends on the location of the abruption).

Retroplacental Bleeding

• Occurs in all cases of abruption.

• Concealed abruption: occurs in $\approx 20\%$ of cases; hemorrhage confined to uterine cavity; detachment may be complete and severe.

• External abruption: blood drains through the cervical os; painful vaginal bleeding; detachment usually less severe if no blood remains in retroplacental space.

Sonographic Findings of Retroplacental Bleeding

• Elevation of the placenta from the uterine wall.

• Retroplacental fluid collection of varying echogenicity (age-dependent), most likely hypoechoic.

• Placenta may appear normal or thickened.

Abnormal Adherence (Placenta Accreta Spectrum)

• Defective decidual formation leading to abnormal placental attachment.

• Uterine scarring is a predisposing factor (chorionic villi may invade C-section scars).

• About two thirds are associated with placenta previa.

• Hysterectomy not recommended due to high maternal hemorrhage risk.

• MRI may be useful to determine extent of invasion (accreta/increta/percreta).

Classification by Villi Extension

• Placenta accrete: chorionic villi in direct contact with myometrium but do not invade.

• Placenta increta: chorionic villi invade the myometrium.

• Placenta percreta: chorionic villi penetrate/perforate the myometrium.

Sonographic Findings of Placental Adherence Abnormalities

• Loss of the normal hypoechoic retroplacental vascular complex.

• Focal basal plate thinning (accrete).

• Increased myometrial thickness and echogenicity (increta).

• Focal myometrial bulge (percreta).

• Color/power Doppler may help.

• Placental growth into bladder (possible sign of invasion).

Intraplacental Lesions

Placental Lakes

• Large pools of maternal venous blood within the placenta.

• Clinically insignificant; appear as anechoic/hypoechoic rounded areas with slow venous flow.

Fibrin Deposition

• Pooling of maternal blood in subchorionic spaces.

• Clinically insignificant; appears as hypoechoic material beneath chorionic surface.

Intervillous Thrombosis

• Caused by fetal bleeding into the intervillous space.

• Increased incidence with Rh incompatibility.

Fetal Membrane Abnormalities

• Common benign types of membranes (not to be confused with amniotic bands):

  • Chorioamniotic Separation

  • Subchorionic Hemorrhage

  • Membranes associated with multiple gestations

  • Intrauterine synechiae

Chorioamniotic Separation (illustrated in fig. 22-22)

Uterine Synechiae (fig. 22-23)

• Examples shown (A, B, C) with SAG/RT views and facial references in the slide.

Gestational Trophoblastic Disease (GTD)

• Includes: complete mole, partial mole, metastatic disease, choriocarcinoma, placenta mesenchymal dysplasia (PMD).

Placental Cysts and Cord Insertion (Fig. 20-17 context)

• Subchorionic or septal cysts of the placenta:

  • Cysts at the site of umbilical cord insertion.

  • Could be multiple cysts (1, 2, 3, 4) on the fetal placental surface.

  • These cysts may resolve spontaneously with a normal delivery.

Intraplacental Lesions (continued)

• Placental Infarcts / Ischemia:

  • Ischemic necrosis of placental villi due to interference with maternal blood flow to the intervillous space.

  • Rare fetal complications with normal uteroplacental circulation; more common in eclampsia/pre-eclampsia.

  • Focal lesions are most prevalent; intervillous thrombosis is also common.

  • Severe cases can cause placental insufficiency and IUGR.

  • Sonographic findings: anechoic or hypoechoic areas; may be small or large; absence of blood flow on color/spectral Doppler.

• Subchorionic (Submembranous) Hematoma:

  • Accumulation of blood beneath the chorion.

  • Sonographic findings depend on age; usually decreases in size on follow-up.

Chorioangioma

• Vascular tumor of placental tissue; occurs in about $1:5000$ pregnancies.

• Large tumors (>$5\ \text{cm}$) may cause polyhydramnios and fetal hydrops.

• Associated with increased maternal serum AFP (MS-AFP).

• Sonographic findings: solid, well-circumscribed placental mass near cord insertion; vascular flow due to trophoblastic tissue.

Umbilical Cord – Review

• Structure: contains 2 arteries and 1 vein, surrounded by Wharton’s jelly and enclosed in amnion.

• Arteries are longer than the vein and twist around the vein in a braided appearance.

• Function: transports blood between fetus and placental circulation.

• Insertion: cord insertion is usually central.

Umbilical Cord Anomalies

• Vessel number: PRUV (persistent right umbilical vein); umbilical vein varix; body stalk anomaly/limb-body wall complex.

• Insertion site: cysts/masses; abnormal position.

• Position: various placements can be diagnostic considerations.

Abnormalities of the Umbilical Cord (Imaging Findings)

• Absence of an umbilical artery or supernumerary vessels.

• A single umbilical artery (SUA) may have as large an umbilical vein on imaging.

• Thorough fetal anatomy evaluation is warranted when abnormalities are detected.

• Findings include: Umbilical Vein Varix; supernumerary vessels; persistent right umbilical vein.

Single Umbilical Artery (SUA) / Bivascular Cord

• Most commonly encountered cord abnormality (~$1\%\text{ of pregnancies}$).

• Etiology: primary agenesis of a single umbilical artery or atrophy of a normally formed artery.

• Isolated SUA does not by itself cause fetal risk but may be associated with other abnormalities.

• Associated abnormalities include:

  • GU anomalies (e.g., unilateral renal agenesis)

  • Trisomies 18 and 13

  • Cardiovascular anomalies

  • CNS anomalies

  • Omphalocele

Placental Cord Insertion Types

• Marginal / Battledore Insertion: cord attaches at the periphery of the placenta; enters at the placental edge.

• Velamentous Insertion: cord attaches to membranes (not directly to placental mass); cord runs beneath the chorion for a distance before reaching the placental edge.

• Associations: may be linked with IUGR, preterm birth, and congenital anomalies.

• Sonographic approach: assess the relationship between cord insertion and placental mass; use color Doppler as needed.

Umbilical Cord Cysts

• Developmental and usually asymptomatic.

• Possible remnants of omphalomesenteric duct (near fetus) or allantoic duct (away from fetus).

• Sonography:

  • Umbilical cord cyst with lack of flow on color/power Doppler.

  • Differentiate from umbilical vein varix using color Doppler.

Abnormalities of the Umbilical Cord – Additional

• Nuchal Cord: cord wrapped around fetal neck.

  • Occurs in roughly $1/5\ (20\%)$ of deliveries; rarely causes fetal issues.

  • Use color Doppler to document.

  • Distinguish true nuchal wrap from cord draping over the neck.

• Vasa Previa: fetal vessels cross the cervical os between cervix and presenting part with membranes intact.

  • Often associated with velamentous cord insertion.

• Cord Prolapse: cord protrudes through cervix or lies beside presenting part with cervix dilated/open.

  • Extremely urgent emergency.

Umbilical Vein Thrombosis

• Causes: torsion, knotting, or compression leading to stasis and thrombosis; may occur after intrauterine transfusion or fetal sampling.

• Higher incidence in infants of diabetic mothers and fetuses with non-immune hydrops.

• Consequences: occlusion prevents perfusion; fetal death is common.

• Sonographic findings: increased echogenicity in lumen; absence of color/spectral Doppler signals in umbilical vessels.

Umbilical Cord Knots

• True knots are rare.

• Associated with monochorionic monoamniotic twins.

• Sonographic appearance: multiple loops of cord in a single scan plane.

Review Questions (Key Points)

• Abruption symptoms: except D) painless second and third trimester bleeding.

• Placenta previa: true statements include that a false positive can occur with anterior placenta if the bladder is overdistended (answer C).

• Placental intervillous thrombosis: caused by thrombosis of a maternal vessel (answer A).

• Chorioangioma associations: may be linked with polyhydramnios, elevated MS-AFP, hydrops; not associated with oligohydramnios (answer D).

• Most common co-existing condition with placenta increta: placenta previa (answer A).

• Match definitions (examples):

  • Battledore placenta: cord inserts at periphery of placenta.

  • Circumvallate placenta: folded/corrugated edge due to membranes forming a central ring.

  • Bi-lobe placenta: separate lobes attached to main placenta.

  • Marginal insertion: cord inserts at placental edge.

  • Velamentous insertion: vessels traverse membranes before reaching placental tissue.

  • Succenturiate placenta: accessory lobe separated from main placental body.

  • Circummarginate placenta: central attachment of membranes without a central ring.

  • Vasa previa: unprotected fetal vessels traverse the lower uterine segment.

Name 3 abnormalities commonly associated with a 2-vessel cord

• Examples:

  • Unilateral renal agenesis (GU anomalies)

  • Trisomies 18/13

  • Cardiovascular anomalies

  • CNS anomalies

  • Omphalocele

Answer Key (summary)

37. D

38. C

39. A

40. D

41. A

42. C / A / D / C / E / D / A / B

43. GU anomalies: unilateral renal agenesis, Trisomy 18/13, cardiovascular anomalies, CNS anomalies, omphalocele