Placental Abruption on Ultrasound: What It Can and Can't Show

Placental abruption is the premature separation of the placenta from the uterine wall. It's an obstetric emergency, and patients often land on your table with painful bleeding, a tender uterus, and a worried care team waiting for your images.

Here's the most important fact for any sonographer to know: ultrasound misses a large share of abruptions. Sensitivity in most studies is only around 25–60%. When you do see a hematoma, it's highly meaningful. When you don't, it means very little. Abruption is a clinical diagnosis.

Why Ultrasound Misses It

• Much of the blood often escapes through the cervix instead of collecting behind the placenta, leaving nothing to image
• Acute hemorrhage can be nearly the same echogenicity as the placenta itself, so it blends in and just looks like a thick placenta
• Posterior placentas are harder to assess, especially late in pregnancy with fetal parts in the way

So never let a negative scan become reassurance, for the patient or for the team.

Where Hematomas Collect

Retroplacental hematoma: a hypoechoic collection of detached blood between the placenta and the uterine wallImage: Nevit Dilmen, CC BY-SA 3.0, via Wikimedia Commons

How Blood Changes Over Time

The appearance of a hematoma depends on its age. This is why acute abruptions are easy to miss and older ones are easier to see.

What to Look For

• A retroplacental collection separating the placenta from the myometrium
• A thickened or heterogeneous placenta: thickness beyond about 5 cm in the third trimester should prompt a closer look
• Rounding or lifting of the placental edge, with fluid tracking under the membranes
• Jello sign: a heterogeneous placenta that jiggles with transducer pressure (seen with fresh clot)
• Echogenic, clotted material in the amniotic fluid near the placenta (a preplacental bleed)
• Absent color Doppler flow within the collection, which helps separate clot from vessels

The Mimics That Fool New Grads

Doppler and patience solve most of these. If you suspect a contraction, keep scanning or come back to that area before calling it.

Scanning Technique

1. Map the entire placenta, including every edge. Marginal bleeds hide at the margins.
2. Evaluate the retroplacental space in at least two planes with color Doppler.
3. Measure any collection in three dimensions and estimate the percentage of placental surface involved.
4. Document placental location and its relationship to the internal os. A previa changes everything about management.
5. Assess the fetus: cardiac activity and heart rate, presentation, and biophysical profile or Doppler if ordered.
6. Check for free fluid in the maternal abdomen if trauma is involved.

What to Document

Example wording to suggest to the interpreting physician:

"Hypoechoic retroplacental collection measuring 6.2 × 4.1 × 2.3 cm along the posterior fundal placenta, without internal color Doppler flow, involving approximately 30% of the placental surface. Fetal heart rate 148 bpm."

Or, when nothing is seen:

"No retroplacental or subchorionic collection identified. Note: a normal ultrasound does not exclude placental abruption."

That second sentence matters. Many radiologists include it routinely, and it protects the patient from false reassurance.

Red Flags: Notify the Team Now

• Any retroplacental hematoma in a symptomatic patient
• Fetal bradycardia or absent cardiac activity
• A collection involving more than about 50% of the placental surface
• A trauma patient, even with a normal-looking placenta (abruption can develop hours later)
• Signs of maternal hemodynamic instability during the exam

Don't wait to finish the full protocol if the fetal heart rate is abnormal or the patient is deteriorating. Follow your department's escalation process right away.

Risk Factors Worth Knowing

Knowing who's at risk sharpens your index of suspicion:

• Hypertension and preeclampsia
• Prior abruption (the strongest predictor)
• Abdominal trauma, including motor vehicle accidents and falls
• Cocaine use and smoking
• Preterm premature rupture of membranes
• Multiple gestation and polyhydramnios (sudden decompression)

Bottom Line

A visible hematoma is significant. An invisible one can still be real. Map the whole placenta, use color Doppler to tell blood from vessels, rescan anything that might be a contraction, and always assess the fetus. Never let your images become the reason someone stops worrying about a clinically suspected abruption.

SonoBuddy is a reference tool, not a diagnostic authority. Final interpretation rests with the interpreting physician.