During your anatomy scan, you may hear:
“Your placenta is lying low.”
Or your ultrasound report may mention:
low-lying placenta
or
placenta previa.
These words can sound frightening—especially when you start wondering whether you will bleed, need activity restrictions, or automatically need a C-section.
But one of the most important things to understand is:
A placenta that is low at the mid-pregnancy anatomy scan may not remain low later in pregnancy.
As the uterus grows, the relationship between the placenta and cervix often changes.
So a low-lying placenta at 20 weeks does not automatically predict where the placenta will be at delivery.
What Is a Low-Lying Placenta?
The placenta attaches to the inner wall of the uterus.
It may be:
- anterior
- posterior
- fundal
- lateral
- or lower within the uterus.
What matters in a low-lying placenta is the relationship between the placental edge and the internal cervical os.
The internal os is the opening of the cervix on the uterine side.
When the placental edge is close to this opening but does not cover it, the placenta may be described as low-lying.
What Is Placenta Previa?
Placenta previa is different.
Low-lying placenta
The placental edge is close to the internal cervical os but does not cover it.
Placenta previa
Placental tissue covers the internal cervical os.
This distinction matters because management and delivery planning may be different.
Older terms such as marginal previa or partial previa may still appear in conversations or older records, but modern reporting generally focuses on whether the placenta covers the os and the measured distance between the placental edge and the os.
How Close Is “Low-Lying”?
A commonly used definition is when the placental edge is within 20 mm (2 cm) of the internal cervical os without covering it.
Ultrasound may therefore report an exact distance, for example:
Placental edge 12 mm from the internal os.
That measurement is much more useful than simply saying:
“The placenta is low.”
How Is the Distance Measured?
The sonographer identifies:
the lower placental edge
and
the internal cervical os.
The shortest distance between them is measured.
Sometimes this can be assessed with transabdominal ultrasound.
But when the relationship is unclear—or an accurate measurement is needed—transvaginal ultrasound may be recommended.
Is Transvaginal Ultrasound Safe With a Low Placenta?
This is a very common concern.
Parents sometimes think:
“If the placenta is near the cervix, won’t the vaginal probe touch it?”
No.
The ultrasound probe remains in the vagina and does not enter the uterus or touch the placenta.
Transvaginal ultrasound is considered the most accurate method for evaluating the relationship between the placenta and internal cervical os when placenta previa or a low-lying placenta is suspected.
It can often provide a much clearer measurement than abdominal imaging.
Why Can the Placenta Seem to “Move Up”?
The placenta does not usually detach and physically crawl upward.
Instead, the uterus changes dramatically as pregnancy progresses.
As the lower uterine segment develops and expands, the placental edge may become progressively farther from the cervix.
This process is sometimes called placental migration, although the term can be misleading.
A better way to think about it is:
The uterus grows around the placenta, changing its position relative to the cervix.
Will My Low-Lying Placenta Move Up?
Often, yes.
A large proportion of placentas identified as low at the mid-trimester anatomy scan are no longer low later in pregnancy.
The likelihood depends on several factors, including:
- how close the placenta is to the cervix
- whether it actually covers the internal os
- anterior versus posterior location
- previous cesarean delivery
- placental anatomy
- gestational age when diagnosed
A placenta that is only slightly low at 20 weeks has a different likelihood of resolving than one substantially covering the cervix.
Does Anterior vs Posterior Placenta Matter?
It can.
Both anterior and posterior placentas can be low-lying.
Studies suggest the probability of persistence may differ depending on placental location and the original distance from the internal os.
But for an individual pregnancy, the most practical information is still:
Where is the placental edge now, and how far is it from the internal os?
The follow-up measurement is more useful than trying to predict the outcome from anterior versus posterior location alone.
When Is the Placenta Checked Again?
If a low-lying placenta or placenta previa is identified at the anatomy scan, a follow-up ultrasound is usually recommended later in pregnancy.
A commonly used approach is reassessment around:
32 weeks
If the placenta remains low, another assessment closer to delivery may be recommended depending on the findings.
Your obstetric team will determine the exact timing.
What Does the Follow-Up Ultrasound Look For?
The main question is simple:
How far is the placental edge from the internal cervical os now?
The sonographer may also evaluate:
- placental location
- cervical region
- fetal presentation
- fetal growth when indicated
- placental appearance
- other findings relevant to delivery planning
If the placenta is now well away from the cervix, the earlier low-lying finding may no longer affect delivery planning.
Does a Low-Lying Placenta Mean I Will Bleed?
Not necessarily.
Some patients with a low-lying placenta or placenta previa experience painless vaginal bleeding, particularly later in pregnancy.
Others never bleed at all.
However, because bleeding can sometimes be significant, vaginal bleeding during pregnancy should be discussed promptly with your healthcare provider.
If bleeding is heavy, persistent, or accompanied by dizziness, weakness, contractions, or other concerning symptoms, urgent medical assessment is appropriate.
Should I Be on Bed Rest?
Not automatically.
Routine bed rest has not been shown to improve outcomes for every patient with a low-lying placenta.
Activity recommendations depend on:
whether bleeding has occurred
whether placenta previa persists
gestational age
and
your individual obstetric situation.
Some patients may receive specific instructions about intercourse, exercise, travel, or activity after bleeding episodes or with persistent previa.
Do not impose strict bed rest on yourself simply because the anatomy scan says the placenta is low.
Ask your obstetric provider what restrictions, if any, actually apply to you.
Does a Low-Lying Placenta Mean I Need a C-Section?
Not necessarily.
This depends heavily on where the placenta is later in pregnancy.
If the placenta moves sufficiently away from the cervix, vaginal delivery may be possible.
If placenta previa persists and the placenta continues to cover the internal os, cesarean delivery is generally required because the placenta blocks the baby’s route through the cervix and vaginal delivery can cause severe bleeding.
For a placenta that remains near—but does not cover—the cervix, delivery planning depends on the measured distance and the individual clinical situation.
Why Does the Exact Distance Matter Near Delivery?
Because:
5 mm from the internal os
is not the same as:
25 mm from the internal os.
As delivery approaches, the placental edge-to-os distance helps the obstetric team assess whether a trial of labor may be appropriate.
There is not one universal number that replaces clinical judgment in every case.
Your obstetrician will interpret the measurement together with:
- bleeding history
- placental location
- fetal presentation
- previous cesarean delivery
- other obstetric factors
What If I Had a Previous C-Section?
This deserves particular attention.
When a placenta is low or previa in someone with a previous cesarean scar, clinicians may look carefully for signs of placenta accreta spectrum (PAS).
PAS refers to abnormal placental attachment to the uterine wall.
But:
Previous C-section + low placenta does not automatically mean placenta accreta.
It means the combination deserves appropriate evaluation.
If ultrasound findings raise concern, referral to maternal-fetal medicine or a specialized center may be recommended.
Does Low-Lying Placenta Affect the Baby’s Growth?
A low placental position by itself does not automatically mean the baby will have growth restriction.
Growth assessment may still be performed for other clinical reasons.
The main issue with a low-lying placenta is generally its relationship to the cervix and the associated risk of bleeding, rather than the placenta simply being “too low” to nourish the baby.
Can I Make the Placenta Move Up?
No specific exercise, sleeping position, food, supplement, or activity can make the placenta move.
You did not cause the placenta to implant low.
And you cannot physically move it by changing your behavior.
What changes is primarily the relationship between the placenta and cervix as the uterus grows.
Time and follow-up imaging tell us what happens.
What If the Placenta Is Still Low at 32 Weeks?
Don’t assume that this automatically means C-section.
The next step depends on:
whether it covers the cervix
how far the placental edge is from the internal os
and
how many weeks remain before delivery.
Some placentas may continue to become more distant from the cervix later in pregnancy.
Your provider may recommend another ultrasound before making the final delivery plan.
Questions to Ask Your Doctor
If your placenta is described as low-lying, useful questions include:
- Is it low-lying or true placenta previa?
- Does the placenta cover the internal cervical os?
- How many millimeters is the placental edge from the os?
- Is the placenta anterior or posterior?
- Should the distance be confirmed transvaginally?
- When should it be checked again?
- Do I need any activity restrictions?
- What should I do if I have vaginal bleeding?
- Does my previous C-section change the evaluation?
- Is there any concern for placenta accreta spectrum?
- At what point will we decide the safest mode of delivery?
The most useful question may be:
“What is the actual distance between the placental edge and the internal os?”
That tells you much more than simply hearing:
“Your placenta is low.”
Key Takeaway
A low-lying placenta at the anatomy scan often does not remain low throughout pregnancy.
The placenta itself does not simply crawl upward.
Instead:
the uterus grows, and the placental edge may become farther away from the cervix.
The most important information is:
Does the placenta cover the internal os?
If not, how far away is the edge?
What does the follow-up ultrasound show?
A low placenta at 20 weeks does not automatically mean placenta previa at delivery, and it certainly does not automatically mean you will need a C-section.
For many parents, the most reassuring words at the follow-up scan are simply:
“The placenta is no longer low.” 🩷
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.
Low placental position is one of those findings where the exact wording and measurement matter. Rather than focusing only on the phrase “low placenta,” ultrasound assessment looks at the relationship between the placental edge and the internal cervical os—and how that relationship changes as pregnancy progresses.
This article is for general educational purposes and does not replace individualized prenatal diagnosis, obstetric or maternal-fetal medicine evaluation, or medical advice from your healthcare provider.
