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Nathan S. Fox, MD

Ultrasound of the Placenta:

What OBGYN Residents Want to Know

Gottesfeld Hohler Memorial FoundationResident Ultrasound Program

August 4, 2019

Financial Disclosures

� None

Objectives

� To learn how to assess placental location using transabdominal and transvaginalultrasound

� A few other things

Why Image the Placenta?

� Location, location, location !!

� Other

� (cord insertion)

� (function)

� (size)

� (morbidly adherent placenta)

� (hematomas)

� (tumors)

TransabdominalAbdominal Ultrasound Pearls

� Start sagittal, midline

� Make sure right of screen points towards her feet

� Check left and right

� Then turn 90 degrees to check transverse

� Make sure right of screen is to her left (as if you are looking at her from her feet)

� Then check superior and inferior

� REMEMBER THE UTERUS IS 3-D !!

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HEAD

ANTERIOR

POSTERIOR

FEET

SAGGITAL

RIGHT

ANTERIOR

POSTERIOR

LEFT

TRANSVERSE

SAGGITAL TRANSVERSE SAGGITAL TRANSVERSE

SAGGITAL TRANSVERSE SAGGITAL TRANSVERSE

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Transvaginal Vaginal Ultrasound Pearls

� Probe neutral position is sagittal

� Start midline

� Then check left and right

� Can assess placental edge in relation to cervix anteriorly / posteriorly

� Not as easy to do laterally (need 3D)

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TV SAGGITAL TA TRANSVERSE

TV SAGGITAL TA TRANSVERSE TV SAGGITAL TA TRANSVERSE

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Previas

� Previa – covers internal cervical os

� Low lying - within 2cm of the internal os

� Formerly known as “Marginal” Previa

� The more important detail is the actual distance from the internal os (or overlapping the os

Previa - Diagnosis

� Must be with transvaginal imaging

� Transabdominal has a 25% false positive rate

� Overdistended bladder

� LUS contraction

� Can gently lift head out of pelvis if needed.

Previas - Resolution

� The placenta only moves in one direction: UP!

� The earlier the diagnosis, the more likely it is to resolve

� The less it overlaps the cervix, the more likely it is to resolve

Morbidly Adherent Placenta Placenta Accreta

Placenta Accreta Spectrum

� Placental lacunae (swiss cheese)

� Disruption of bladder line

� Loss of clear zone (behind placenta)

� Myometrial thinning

� Abnormal vascularity

� Placental bulge

� Exophytic mass

Lacunae

Myometrial thinning

Focal mass

Increased vascularity

Normal

Accreta

� Ultrasound is not diagnostic

� (Neither is MRI)

� Ultimately, it is about the SUSPICION of accreta and preparing for it

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CS #1 CS #2 CS #3 CS #4 CS #5 CS #6+

Overall 0.2% 0.3% 0.6% 2.1% 2.3% 6.7%

No Previa 0.03% 0.2% 0.1% 0.8% 0.8% 4.7%

Yes Previa 3.3% 11% 40% 61% 67% 67%

Likelihood of Accreta

Silver et al, OBG 2008

Velamentous Cord Insertion

Normal Velamentous Velamentous Cord Insertion

� Risk of IUGR

� Due to velamentous cord itself?

� Due to abnormal placenta in general?

� Due to overlapping risk factors?

� Risk of vessel compression in labor

� Risk of vasa previa

Vasa Previa

Vasa Previa

� Risk Factors:

� Resolved previa

� Velamentous cord

� Succenturiate lobe

� (IVF, Twins)

� Diagnosis

� Color!!!

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