The baby looked fine.
The measurements were reassuring.
Then, while scanning the placenta, the sonographer paused over a small dark area.
You may hear:
“There’s a cyst on the placenta.”
And suddenly the reassuring ultrasound feels much less reassuring.
Parents often ask me:
Is it a tumor?
Can it affect blood flow to my baby?
Will it get bigger?
Is this the same thing as a placental lake?
The first thing to know is:
A small isolated placental cyst is often not a dangerous finding.
But not every cyst-like structure in the placenta means the same thing.
Its location, size, appearance, blood flow, and relationship to the umbilical cord matter.
What Does a Placental Cyst Look Like?
On ultrasound, a simple placental cyst typically appears as a:
well-defined, fluid-filled, anechoic or nearly anechoic area.
In plain language:
it looks dark because simple fluid does not produce many internal echoes.
The wall may be thin and smooth.
But seeing a dark space in the placenta does not automatically tell us what it is.
That is where careful scanning matters.
Where Are Placental Cysts Usually Found?
Some cysts are seen on or immediately beneath the fetal surface of the placenta, under the chorionic plate.
These are often described as:
subchorionic placental cysts
or
chorionic plate cysts.
They may occur anywhere along the fetal placental surface.
One detail I pay particular attention to is:
How close is the cyst to the umbilical cord insertion?
That location can sometimes matter more than the fact that a cyst exists.
Is a Placental Cyst the Same as a Placental Lake?
No.
This is one of the most useful distinctions for parents.
A placental lake is a maternal blood-filled space within the intervillous portion of the placenta.
A placental cyst is a cystic structure associated with the placental surface or tissue.
They can both look dark on grayscale ultrasound.
But they are not necessarily the same structure.
How Does Color Doppler Help?
If I see a cyst-like area, one of my first questions is:
“Is there blood flow inside it?”
A simple cyst generally should not show internal vascular flow.
Color Doppler can help distinguish it from:
- blood-filled placental spaces
- vascular placental lesions
- fetal vessels
- other structures near the cord insertion
This is especially useful when the grayscale image alone is ambiguous.
Placental Cyst vs Chorioangioma
This distinction follows naturally from the previous topic.
Placental cyst
Usually appears predominantly fluid-filled and lacks internal blood flow.
Chorioangioma
A benign vascular placental tumor that may demonstrate internal or feeding vessels on Color Doppler.
So when a placental lesion is seen:
vascularity can completely change the differential diagnosis.
But Doppler is interpreted together with morphology and location—not by color alone.
Does the Size of the Cyst Matter?
Yes, but size is not the whole story.
A small isolated cyst with:
- normal fetal growth
- normal placental appearance
- reassuring cord insertion
- no other abnormalities
may have little clinical significance.
A larger cyst—or multiple cysts—may deserve closer attention, particularly when located near the umbilical cord insertion.
Published literature has described associations between larger or multiple placental surface cysts and fetal growth problems in some pregnancies.
But:
a cyst does not automatically mean fetal growth restriction will occur.
Why Does the Cord Insertion Matter?
Imagine a large cyst sitting immediately beside the point where the umbilical cord enters the placenta.
That creates a different anatomical situation from:
a tiny cyst at the far edge of the placenta.
A sufficiently large lesion near the cord insertion could theoretically affect or distort nearby fetal vessels.
This is why I don’t just measure the cyst.
I look at:
where it is.
What Does the Sonographer Look At?
When a placental cyst is identified, useful questions during the scan include:
How many are there?
One or multiple?
How large is it?
A few millimeters or several centimeters?
Where is it?
Near the cord insertion or away from it?
What is inside?
Completely anechoic or containing internal echoes?
Is there blood flow?
Color Doppler can help.
What does the rest of the placenta look like?
Normal or abnormal?
And then I go back to the baby.
Why Do We Go Back to the Baby?
Because the significance of a placental finding is rarely determined by the placenta alone.
I want to know:
Is the baby growing normally?
The ultrasound may assess:
- abdominal circumference
- head circumference
- femur length
- estimated fetal weight
If a placental cyst is large or persistent, interval fetal growth may become more relevant.
Can a Placental Cyst Grow?
Yes, some can change in size.
A cyst may remain stable, become larger, or occasionally become less conspicuous.
That’s why a follow-up scan may be useful when the lesion is large or when there are other concerns.
But repeatedly measuring a tiny incidental cyst is not always necessary.
Management depends on the complete clinical picture.
What If There Are Several Cysts?
Multiple placental cysts deserve a little more context than one tiny isolated cyst.
The examiner may pay closer attention to:
- placental morphology
- fetal growth
- cord insertion
- Doppler findings when indicated
- associated fetal or maternal findings
Again, the finding is not interpreted from the number of cysts alone.
Could It Be a Hematoma Instead?
Sometimes a blood collection can appear cystic.
The appearance of a hematoma changes depending on its age.
Fresh blood, organizing clot, and older collections can have different echogenicity.
Clinical history can also help.
For example:
vaginal bleeding
or
a known earlier subchorionic hematoma
may change how a cystic placental area is interpreted.
Is This the Same as a Subchorionic Hematoma?
No.
The words sound similar, which causes a lot of confusion.
Subchorionic cyst
A cystic lesion associated with the chorionic plate/placental fetal surface.
Subchorionic hematoma
A collection of blood in a subchorionic location.
They are not interchangeable diagnoses.
Ultrasound appearance and clinical history help distinguish them.
Can a Placental Cyst Hurt the Baby?
Most small isolated placental cysts do not directly harm the fetus.
Concern increases when the finding is:
unusually large,
multiple,
close to the cord insertion,
or
associated with abnormal fetal growth or other placental findings.
That’s why the question isn’t simply:
“Is there a cyst?”
It is:
“Is there any evidence that this cyst is affecting placental or fetal wellbeing?”
Does It Mean My Placenta Is Failing?
No.
A placental cyst does not automatically indicate placental insufficiency.
If placental function is a concern, clinicians consider information such as:
- fetal growth
- amniotic fluid
- fetal movement
- maternal conditions
- Doppler findings when indicated
A single cyst cannot answer those questions.
Do I Need Doppler Ultrasound?
Not necessarily.
Color Doppler may be used locally to characterize the lesion and determine whether it contains blood flow.
Formal fetal Doppler studies—such as umbilical artery Doppler—are different.
Those may be indicated if there is:
fetal growth restriction
or another clinical reason to assess placental circulation.
A tiny isolated cyst does not automatically require intensive Doppler surveillance.
Will I Need Another Ultrasound?
Sometimes.
Follow-up may be considered when:
- the cyst is relatively large
- multiple cysts are present
- it lies near the cord insertion
- fetal growth needs reassessment
- the diagnosis is uncertain
- other placental abnormalities are present
If it is small and isolated with an otherwise reassuring examination, management may be much simpler.
Does a Placental Cyst Mean I Need a C-Section?
No—not by itself.
A placental cyst does not automatically determine how you will deliver.
Delivery planning depends on:
- fetal wellbeing
- fetal growth
- gestational age
- placental and cord findings
- maternal conditions
- the overall obstetric situation
Many small placental cysts have no effect on delivery planning at all.
A Realistic Way to Think About It
Consider these two ultrasound findings.
Case A
A 1 cm simple cyst on the placental surface.
Away from the cord insertion.
No internal blood flow.
Baby growing normally.
Everything else reassuring.
Case B
A large multiloculated cystic lesion close to the cord insertion.
Nearby vessels appear displaced.
Fetal growth is falling across percentiles.
Both could initially be described to a parent as:
“a cyst on the placenta.”
But they clearly do not mean the same thing.
That’s why a diagnosis should never stop at the label.
Questions to Ask Your Doctor
If a placental cyst is mentioned, I would ask:
- How large is the cyst?
- Is there only one?
- Where is it located?
- Is it close to the umbilical cord insertion?
- Does it contain any blood flow on Color Doppler?
- Does the rest of the placenta look normal?
- Is my baby growing normally?
- Could this be a placental lake or hematoma instead?
- Do I need another growth ultrasound?
- Does this change my pregnancy management?
But the question that puts everything into perspective is:
“Is this an isolated cyst, or is there anything else on the scan that concerns you?”
Key Takeaway
Finding a cyst on the placenta can sound much more frightening than the ultrasound actually looks.
Small isolated placental cysts are often uncomplicated findings.
When deciding whether a cyst matters, I care about:
size
number
location
relationship to the cord insertion
Color Doppler appearance
and most importantly:
how the baby is doing.
A placental cyst is not automatically a tumor.
It is not automatically a placental lake.
And it does not automatically mean the placenta is failing.
Sometimes a small dark circle really is just one small part of an otherwise completely reassuring ultrasound. 🩷
About the Author
This article was written by a sonographer with over 20 years of hands-on clinical ultrasound experience, including fetal, breast, and thyroid imaging.
When I find a cystic area in the placenta, I rarely start by worrying about the name. I first change the scanning angle, look for internal echoes, turn on Color Doppler, and find the cord insertion. Then I check the fetus. Those few steps usually tell me much more than simply writing “placental cyst” on the image.
This article is for general educational purposes and does not replace individualized prenatal diagnosis, maternal-fetal medicine evaluation, fetal surveillance, or medical advice from your healthcare provider.
