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Vasa Previa

Also known as Vasa praevia. Diagnosed by ultrasound around 18 to 26 weeks; delivery planned 34 to 37 weeks.

Vasa previa is a rare condition in which some of the baby's blood vessels run through the membranes across or very near the cervix, stripped of the protection the umbilical cord and placenta normally give them. The stakes are stark but hopeful: undiagnosed, those vessels can tear when the water breaks and the baby can lose blood dangerously fast; found ahead of time on ultrasound and delivered by planned cesarean before labor, almost all babies do well. Finding it is everything, and it can be found.

Know the warning signs When to call a provider
How common
About 1 in 2,500
Rare overall; more common, about 1 in 200, after IVF.
When
Found at 18 to 26 weeks
Diagnosed on ultrasound; delivery planned by cesarean at 34 to 37 weeks.
Urgency
Planned closely
Managed with a careful plan; bleeding when the water breaks is a true emergency.
Outlook
Excellent if diagnosed
Around 97% of babies survive when it is found before birth.

Understanding it

What is vasa previa?

A baby's blood vessels normally travel shielded, sheathed inside the umbilical cord and buried in the placenta. In vasa previa, some of those fetal vessels instead run bare through the thin membranes, crossing or sitting within a couple of centimeters of the cervix's internal opening, right in the path of birth.

That position is the entire danger. When your water breaks, the membranes rupture, and vessels lying across the cervix can tear at the same instant. Because the blood in them is the baby's, and a baby's total blood volume is small, the loss is fast and life-threatening: fetal bleeding, not yours, so the danger falls on the baby.

Two setups account for most cases. In one, the umbilical cord inserts into the membranes instead of the center of the placenta, a velamentous cord insertion, leaving vessels to run unprotected to the placenta. In the other, the placenta has an extra lobe, and the vessels bridging the lobes cross the cervix. Both are likelier with IVF, a low-lying placenta or previa (even one that later rises), and twin pregnancies.

One fact changes everything: vasa previa can be seen on ultrasound before birth, usually a transvaginal scan with color Doppler to light up the blood flow. Caught ahead of time, with a cesarean scheduled before labor, the outlook is excellent; missed and discovered only when bleeding starts, it is far worse. That contrast is why screening the at-risk and planning delivery matter so much.

Symptoms

What are the symptoms?

Vasa previa usually causes no symptoms and is found on ultrasound. When it does cause symptoms, or when a vessel tears, it is an obstetric emergency.

Early signs

  • Usually none; it is typically silent and found on a routine or targeted ultrasound
  • Occasionally painless vaginal bleeding in the second or third trimester
  • Painless vaginal bleeding especially when the water breaks, which is an emergency
  • Most cases are caught before any symptoms appear

Emergency signs — call 911

  • Vaginal bleeding when the water breaks, an emergency for the baby
  • Any painless vaginal bleeding in the second half of pregnancy: go in to be evaluated
  • Your water breaking with known vasa previa: call 911 or go in immediately
  • Reduced or unusual fetal movement with known vasa previa

Why it matters

Risks to you and baby

Fetal bleeding at membrane rupture

The central danger: the exposed vessels tear when the water breaks and the baby loses blood very fast. Preventing this one event, by delivering before labor, is what the entire plan is built around.

The outcome hinges on diagnosis

The defining fact of vasa previa. Diagnosed before birth and delivered by planned cesarean, around 97% of babies survive; undiagnosed and found only at bleeding, fetal death approaches 56% to 60%. Finding it changes everything.

Prematurity from planned early delivery

Delivering early, at 34 to 37 weeks to stay ahead of labor, leaves the baby somewhat premature. It is a deliberate trade: the manageable risks of late-preterm birth against the catastrophic risk of a torn vessel.

Little maternal risk from the condition itself

Vasa previa threatens the baby, not you. The cesarean carries the usual surgical considerations, but the condition itself poses little maternal risk.

How it's found

How is it diagnosed?

Vasa previa is diagnosed by ultrasound, specifically a transvaginal scan with color Doppler, which shows the vessels crossing near the cervix. Prenatal ultrasound catches the large majority of cases.

Transvaginal ultrasound with color Doppler

Color Doppler lights up blood flow, revealing fetal vessels running over or within about 2 centimeters of the internal cervical opening, bare of cord or placenta.

Assessing the cord and placenta

The scan checks where the cord inserts and whether the placenta has an extra lobe, the two anatomic setups that lead to vasa previa.

Targeted screening of at-risk pregnancies

People with a low-lying placenta, velamentous cord insertion, an accessory placental lobe, IVF, or twins get a focused look, since most cases have an identifiable risk factor.

Usually seen at the anatomy scan around 18 to 26 weeks, with confirmation in the early third trimester, around 28 to 32 weeks.

Treatment

How is it managed?

Once diagnosed, the plan is built entirely around delivering by cesarean before labor and before the membranes can rupture, with close monitoring in the weeks leading up to it.

Treatment paths

Care is proactive and scheduled. Steroids around 28 to 32 weeks mature the baby's lungs ahead of the early delivery. Many providers admit you around 30 to 34 weeks for close monitoring, so an immediate cesarean is possible if bleeding or labor starts. Fetal monitoring, such as non-stress tests, runs regularly.

Monitoring

Regular fetal monitoring and, often, hospitalization in the weeks before delivery allow a fast response if anything changes.

Can it recur?

Vasa previa arises from the particular cord and placental anatomy of a given pregnancy, and there is no established recurrence rate. It is not thought to predictably repeat, though a future pregnancy would still be screened, especially if risk factors like IVF are present again.

What you can do

Can it be prevented?

  • There is no way to prevent it forming

    Vasa previa comes from how the cord and placenta formed, which cannot be prevented. What prevents the emergency is finding it before birth and planning delivery around it.

  • Get screened if you have risk factors

    A low-lying placenta or previa, a velamentous cord insertion, an extra placental lobe, IVF, or twins all warrant a targeted Doppler look at the cervix, since that is how vasa previa is caught in time.

  • Follow the delivery plan exactly

    Once diagnosed, the planned early cesarean, hospitalization, and monitoring are what keep your baby safe. Keeping every appointment is the protection.

  • Know your emergency instructions

    If you have vasa previa and your water breaks or you bleed, it is an emergency: call 911 or go straight to labor and delivery, and tell them you have vasa previa.

Who is more at risk

Risk factors

Velamentous cord insertion
When the umbilical cord attaches to the membranes rather than the center of the placenta, vessels travel unprotected and can end up crossing the cervix.
Low-lying placenta or placenta previa
A placenta near or over the cervix, even one that later moves up as pregnancy progresses, raises the risk of vasa previa.
About 60% of cases had a low-lying placenta or previa on the second-trimester scan.
IVF and assisted reproduction
Pregnancies conceived through IVF have a notably higher rate of vasa previa.
Roughly 1 in 200 after IVF, versus about 1 in 2,500 overall.
An extra placental lobe
A bilobed placenta or an accessory (succenturiate) lobe leaves vessels bridging between the lobes that can cross the cervix.
Twin or multiple pregnancy
Carrying more than one baby raises the chance of the cord and placental variations that lead to vasa previa.

Do not wait

When to call your provider or 911

  • If you have known vasa previa and your water breaks, call 911 or go to labor and delivery immediately, and tell them you have vasa previa.
  • Seek emergency care for any vaginal bleeding in the second half of pregnancy, especially painless bleeding.
  • Go in right away for reduced or unusual fetal movement if you have a known vasa previa.
  • Ask about targeted screening if you have a low-lying placenta, velamentous cord insertion, an extra placental lobe, IVF, or twins.
  • Confirm your delivery plan and your exact instructions for what to do if labor or bleeding starts early.

Talking to your team

Questions to ask your provider

  • Do my ultrasound findings show vasa previa, and which type?
  • When will you confirm the diagnosis with a follow-up scan?
  • When would you plan my cesarean, and will steroids be given first?
  • Will I need to be admitted to the hospital before delivery, and when?
  • What exactly should I do if my water breaks or I start bleeding?
  • Will the delivery be at a hospital that can transfuse the baby if needed?

Keep reading

More on vasa previa

All pregnancy guides articles

Good to Know

Vasa Previa FAQs

Common questions about vasa previa, answered.

What exactly is vasa previa?

It is when some of your baby's blood vessels run bare through the membranes and cross, or sit very close to, the cervix, instead of safely inside the umbilical cord and placenta. Because they sit in the path of delivery, they can tear when the water breaks. Found ahead of time, it is managed with a planned cesarean.

How serious is it?

It can be very serious for the baby if undiagnosed, because a torn vessel bleeds the baby fast. But the outcome hinges almost entirely on whether it is found before birth: diagnosed and delivered by planned cesarean, the large majority of babies do well; missed, the danger is grave. That is why screening and a delivery plan matter so much.

How is it found?

On ultrasound, usually a transvaginal scan with color Doppler, which reveals the vessels crossing near the cervix. It is often seen at the anatomy scan around 18 to 26 weeks and confirmed later. Screening at-risk pregnancies catches the large majority of cases.

Why do I have to deliver early?

To stay ahead of labor. The danger comes when the membranes rupture, so delivery is by planned cesarean at 34 to 37 weeks, before labor typically begins, with steroids first to mature the baby's lungs. It trades the manageable risks of a slightly early birth for avoiding a torn vessel.

Will I need to be in the hospital before delivery?

Often, yes. Many providers admit you around 30 to 34 weeks for close monitoring, so an immediate cesarean is possible if bleeding or labor starts. The exact timing is individualized to your situation.

Is the bleeding dangerous to me or the baby?

To the baby. Those vessels carry the baby's blood, so if they tear it is the baby who bleeds, and a baby's small blood volume means it happens fast. This is why any bleeding, and especially your water breaking, is treated as a fetal emergency.

Can vasa previa be prevented?

The condition itself cannot be prevented, since it comes from how the cord and placenta formed. What can be prevented is the emergency: finding it on ultrasound before birth and delivering by planned cesarean before labor. That is the whole strategy, and it works.

Will it happen in my next pregnancy?

There is no established recurrence rate, and vasa previa is not thought to predictably repeat, since it depends on each pregnancy's specific anatomy. A future pregnancy would still be screened, particularly if risk factors like IVF or an extra placental lobe are present again.

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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