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Placental & bleeding Call your provider

Placenta previa

Also known as Low-lying placenta. Confirmed in the third trimester; often first seen at the 20-week scan.

In placenta previa, the placenta lies low and covers or nearly reaches the cervix, the opening a baby passes through during a vaginal birth. Its hallmark is bright red vaginal bleeding, usually painless, in the second half of pregnancy. Most low placentas seen early climb up and out of the way as the uterus grows. When previa persists, careful monitoring and a planned cesarean keep the great majority of pregnancies safe.

Know the warning signs When to call a provider
How common
About 1 in 200 at term
Many more are low-lying early and resolve on their own.
When
Second half of pregnancy
Often first noted at the 20-week scan, confirmed near 32 weeks.
Urgency
Call your provider
Any bleeding needs a call; heavy bleeding is an emergency.
Outlook
Good with planning
A scheduled cesarean and monitoring keep most pregnancies safe.

Understanding it

What is placenta previa?

The placenta usually implants high on the uterine wall, well clear of the cervix. In previa it settles low, covering all or part of the cervix's internal opening. Location is the whole problem: as the lower uterus stretches and thins late in pregnancy, the vessels anchoring the placenta can tear and bleed, and the placenta itself blocks the exit, so a vaginal birth is unsafe.

A low placenta found early is usually not permanent, which is worth holding onto. As the uterus grows, most low-lying placentas ride up and away from the cervix, a shift called placental migration. Nearly 90% of those flagged as low at the 20-week scan have resolved by the third trimester. So an early low placenta is watched, not treated as a crisis, and rechecked on a later scan.

True previa announces itself with painless bright red bleeding in the second half of pregnancy. That painless quality separates it from placental abruption, where bleeding comes with pain and a tense, tender uterus. About a third of people bleed not at all, and previa turns up only on ultrasound.

When previa persists, the plan centers on shielding you from heavy bleeding and delivering safely: avoid anything that could provoke a bleed, watch closely, and schedule a cesarean before labor starts. Outcomes with this approach are generally very good.

Symptoms

What are the symptoms?

The hallmark is sudden, painless, bright red bleeding in the second half of pregnancy. Some people have no symptoms and it surfaces on a scan. Because a bleed can turn serious, any bleeding is a reason to be seen.

Early signs

  • Painless bright red vaginal bleeding after 20 weeks
  • Bleeding that may start, stop, and start again
  • Bleeding sometimes triggered by sex or a vaginal exam
  • Sometimes mild cramping or contractions
  • In about a third of cases, no bleeding at all

Emergency signs — call 911

  • Any vaginal bleeding in the second half of pregnancy, which needs an immediate call
  • Heavy vaginal bleeding, which means going to the hospital right away
  • Bleeding along with contractions or belly pain
  • Feeling faint, dizzy, or having a racing heart with bleeding

Why it matters

Risks to you and baby

Bleeding

The main risk is bleeding, from light spotting to heavy, life-threatening hemorrhage, and it can strike without warning. That unpredictability is why any bleeding is taken seriously and why persistent previa is watched so closely.

Preterm birth

Significant bleeding may force an early delivery to keep you both safe. When that looks likely, steroids are given to mature your baby's lungs.

A cesarean birth

A placenta covering the cervix makes vaginal birth unsafe, so delivery is by cesarean, planned in advance and usually before labor starts.

Placenta accreta

Previa raises the chance the placenta is also attached too deeply, called placenta accreta, particularly after a prior cesarean. Ultrasound checks for it, and if found it reshapes the delivery plan.

Your baby's outlook

With monitoring and a planned delivery, most babies do well. The main risk to your baby is prematurity, if heavy bleeding forces an early birth.

How it's found

How is it diagnosed?

Ultrasound diagnoses previa, showing exactly where the placenta sits relative to the cervix. A low placenta found early is rechecked later to see whether it has moved.

Transvaginal ultrasound

The most accurate view of the placenta's position and its distance from the cervical opening. Done carefully, it is safe in previa.

Anatomy (20-week) ultrasound

Often where a low-lying placenta is first noticed. Most resolve, so it is a starting point, not a verdict.

Follow-up ultrasound

A repeat scan around 28 to 32 weeks confirms whether the placenta has moved or previa persists, and looks for signs of placenta accreta.

Often first seen at the 20-week scan, then confirmed or cleared later. A digital vaginal exam is avoided when previa is suspected, since it can provoke bleeding.

Treatment

How is it managed?

Care hinges on whether previa persists and whether you are bleeding. The goal is to prevent heavy bleeding and deliver safely by a planned cesarean before labor.

Treatment paths

An early low placenta mainly needs a follow-up scan, since most resolve. Persistent previa usually calls for pelvic rest (no sex, no tampons, nothing that could provoke bleeding) and prompt evaluation of any bleed, with hospitalization for monitoring during episodes. If preterm delivery looms, steroids mature your baby's lungs, and magnesium sulfate may be added for neuroprotection if birth is very early.

Monitoring

Repeat ultrasounds track the placenta's position and screen for accreta. Any bleeding is assessed promptly, and delivery timing is tailored to you.

Can it recur?

The chance of previa in a future pregnancy is modestly higher than average, around 2% to 3%. Limiting avoidable cesareans and other uterine surgery, and not smoking, lowers the risk of both previa and the more serious accreta next time.

What you can do

Can it be prevented?

  • It cannot be directly prevented

    Because the cause of low implantation is not fully understood, previa cannot be prevented outright.

  • Limit avoidable uterine surgery

    Each cesarean and uterine surgery raises the risk of previa and accreta later, so skipping medically unnecessary procedures protects future pregnancies.

  • Do not smoke

    Smoking is a risk factor for previa, one more reason to quit before and during pregnancy.

Who is more at risk

Risk factors

A prior cesarean or uterine surgery
Scarring from a previous cesarean, fibroid surgery, or a D&C is a leading risk factor.
A prior placenta previa
Having had previa raises the odds of it recurring.
Carrying multiples
A twin or higher-order pregnancy has a larger placenta, increasing the chance it lies low.
Age and smoking
Advanced maternal age, smoking, and cocaine use all raise the risk.
Assisted reproduction
Pregnancies conceived through IVF have a somewhat higher rate of previa.

Do not wait

When to call your provider or 911

  • Go to the hospital right away for heavy vaginal bleeding, or call 911 if you also feel faint, dizzy, or have a racing heart.
  • Call your provider immediately for any vaginal bleeding in the second half of pregnancy, even if it stops on its own.
  • Call for bleeding that comes with contractions, cramping, or belly pain.
  • If you have known previa, follow your provider's guidance on pelvic rest and activity, and report any new bleeding.
  • Keep your follow-up ultrasound appointments, which confirm whether the placenta has moved and screen for accreta.

Talking to your team

Questions to ask your provider

  • Does my placenta still cover the cervix, or has it moved up?
  • When will I have a follow-up scan to check its position?
  • What activity restrictions or pelvic rest do you recommend?
  • What is the plan and likely timing for my cesarean?
  • Do I have any signs of placenta accreta?
  • What bleeding should send me to the hospital, and what should I do if it happens?

Keep reading

More on placenta previa

All pregnancy guides articles

Good to Know

Placenta previa FAQs

Common questions about placenta previa, answered.

My 20-week scan showed a low placenta. Does that mean I will need a cesarean?

Not necessarily. Most low placentas found at 20 weeks move up and away from the cervix as the uterus grows, and a follow-up scan later confirms it. Only if the placenta still covers the cervix near term is a cesarean needed.

Is the bleeding dangerous even if it does not hurt?

It can be. The painless quality is typical, but a bleed can turn heavy fast. Any bleeding in the second half of pregnancy warrants an immediate call, and heavy bleeding means going to the hospital right away.

Can I have sex or exercise?

With persistent previa or any bleeding, your provider will likely advise pelvic rest: no sex, tampons, or vaginal exams, and often limits on strenuous activity. The aim is to avoid anything that could provoke a bleed. Ask what is safe for you.

Will I definitely need a cesarean?

If the placenta still covers the cervix at delivery, yes, and it is planned in advance, usually around 36 to 37 weeks. If it has moved up enough, a vaginal birth may be possible.

Is my baby in danger?

With monitoring and a planned delivery, most babies do well. The main risk is being born early if heavy bleeding forces it, which is why steroids are given ahead of time when preterm birth looks likely.

What is the difference between previa and placental abruption?

Previa typically causes painless bright red bleeding because the placenta sits over the cervix. Placental abruption, where the placenta separates from the wall, usually causes painful bleeding with a tense, tender uterus. Both need urgent evaluation, but the pattern helps tell them apart.

Will it happen again in my next pregnancy?

The chance is modestly higher than average, around 2% to 3%. Avoiding unnecessary uterine surgery and not smoking lowers the risk of previa and the more serious accreta next time.

What is placenta accreta, and am I at risk?

Placenta accreta is when the placenta attaches too deeply and does not detach normally after birth. Previa raises that risk, especially after a prior cesarean. Your provider looks for it on ultrasound and plans delivery accordingly if found.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

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