Abnormal Placental Margin
Roya Sohaey, MD
DIFFERENTIAL DIAGNOSIS
Common
Marginal Placental Abruption
Circumvallate Placenta
Synechiae
Marginal Cord Insertion
Less Common
Chorioamniotic Separation
Placenta Accreta Spectrum
Rare but Important
Vasa Previa
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Always scan entire placental surface
Doppler essential for evaluating placental pathology
Document cord insertion site
Marginal cord insertion versus velamentous cord insertion
Are branching vessels on surface of placenta or submembranous?
Marginal insertion if all vessels on surface of placenta
Velamentous cord insertion if any fetal vessel is submembranous
Vasa previa if fetal vessels are near cervix
Vessels beyond uterine wall with accreta
Look for invasion of bladder
Synechiae may show flow
Pulsed Doppler differentiates fetal vessels from maternal
Fetal arterial flow similar to cord Doppler waveform
Helpful Clues for Common Diagnoses
Marginal Placental Abruption
Most common type of placental abruption
Detachment of edge of placenta
Raised placental margin seen in 50%
Submembranous blood
Appearance of hematoma related to age
Acute blood can be isoechoic to placenta
Becomes hypoechoic with time
Sonolucent if old
Circumvallate Placenta
Membranes attach to fetal surface of placenta instead of villous margin
Caused by discrepant size between chorion and basal plates
Placental marginal “shelf” seen with ultrasound
Elevated margin of placenta
Placenta lifted towards cord insertion site
Placenta edge appears to be floating free in fluid
Short bands of tissue
Extend from placental margin to placental margin
Thicker earlier in pregnancy
Tissue may become fibrosed
Synechiae
Fibrous band in uterus
Secondary to uterine scar
Amnion and chorion drape over synechiae
Long bands of tissue
Extend from uterine wall to uterine wall
Bands are thicker earlier in pregnancy
Stretch thin as uterus grows
Fetus moves freely around synechia
Differentiates from amniotic bands
Placental implantation common
Edge of placenta lifted onto synechia
Follow course of synechia to show uterine attachment
Doppler may show flow in synechia
Marginal Cord Insertion
Eccentric placental cord insertion
Within 2 cm of placental margin
Battledore placenta is a subtype
Thick placenta
Small surface area of attachment
Higher risk for abruption
At risk for becoming velamentous cord insertion
Cord insertions < 5 mm from placental margin
Placenta may involute and leave vessels subplacental
At risk for vasa previa if vessels near cervix
Helpful Clues for Less Common Diagnoses
Chorioamniotic Separation
Persistent unfused amnion after 16 wks
Primary nonfusion
Post amniocentesis
Ultrasound findings
Thin amniotic membrane separate from uterine wall
Associations with nonfusion
Trisomy 21
Genitourinary anomalies
Oligohydramnios
Placenta Accreta Spectrum
Placenta grows beyond endometrial lining
Associated with multiple prior cesarean sections
Ultrasound and MR findings
Loss of subplacental myometrium
Vessels or placental tissue beyond uterus
Distended vascular lacunae
Helpful Clues for Rare Diagnoses
Vasa Previa
Submembranous fetal vessels within 2 cm of internal cervical os
Clinical scenarios
Succenturiate lobe crossing vessels
Velamentous cord insertion near cervix
Transvaginal Doppler essential for diagnosis
Color Doppler shows crossing vessels
Pulsed Doppler to prove fetal vascularity
Other Essential Information
Size of abruption is associated with outcome
Excellent prognosis if < 30% detached
Poor prognosis if > 50% detached
Look for other areas of abruption once one abruption is seen
Retroplacental, preplacental, multiple margins
Rare complications of significant circumvallate placenta
Abruption
Intrauterine growth restriction
↑ Risk if > 2/3 of margin involved
Look for fetal anomalies if chorioamniotic separation seen
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