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Vasa Previa Bleeding

What is Vasa previa bleeding?

Vasa previa is a rare obstetric condition in which fetal blood vessels run across or near the internal opening of the cervix (the os) and are unprotected by the placenta or the umbilical cord. When the membranes rupture during labor or the cervix begins to thin, these vessels can tear, causing vasa previa bleeding. The bleeding is fetal in origin, not maternal, and can lead to rapid loss of oxygen and blood volume for the baby.

The condition occurs in roughly 1 in 2,500–5,000 pregnancies, but the risk of severe fetal compromise is high if it is not identified before labor begins. Early detection with ultrasound, combined with planned delivery, dramatically improves outcomes.<sup>1</sup>

Common Causes

Vasa previa is not caused by a single event; rather, it results from an abnormal placement of fetal vessels during placental development. The most frequent scenarios include:

• Velamentous cord insertion – the umbilical cord attaches to the fetal membranes rather than directly to the placenta, leaving vessels exposed.
• Bilobed or multilobed placenta – separate placental lobes are connected by membrane bridges containing fetal vessels.
• Succenturiate (accessory) lobe – a small extra lobe of placenta is linked to the main placenta by membranes with vessels that may cross the cervical os.
• Low-lying placenta (placenta previa) that partially folds over the cervix.
• Multiple gestations – twins or higher-order multiples increase the chance of abnormal vessel placement.
• Assisted reproductive technologies (ART) – in vitro fertilization and related techniques have been associated with a higher prevalence of velamentous insertion.
• Previous uterine surgery – scarring can alter placental implantation patterns.
• Maternal smoking – nicotine may affect placental vascular development.
• Advanced maternal age (≥35 years) – associated with higher rates of placental anomalies.
• Familial predisposition – rare reports suggest a genetic component to abnormal cord insertion.

Associated Symptoms

Because the bleeding originates from fetal vessels, mothers often experience symptoms that differ from typical third‑trimester bleeding. The most common accompanying signs are:

• Bright red vaginal bleeding that starts suddenly, usually after the membranes rupture (rupture of membranes, ROM) or with cervical dilation.
• Absence of pain (painless bleeding) – unlike placental abruption, which is usually painful.
• Fetal heart rate (FHR) abnormalities – sudden decelerations, bradycardia, or loss of variability within minutes of bleeding.
• Uterine tenderness is usually **not** present.
• Maternal vital signs often remain stable because the blood loss is fetal, not maternal.
• In some cases, the mother may notice a “wet” sensation or fluid loss before the bleed, indicating that the membranes have ruptured.

When to See a Doctor

Any vaginal bleeding in the third trimester warrants prompt evaluation, but the following points should trigger immediate contact with your obstetric care provider or a call to emergency services:

• Bleeding that starts after your water breaks (spontaneous or artificial rupture of membranes).
• Bleeding that is bright red, gushes, or increases in volume quickly.
• Any change in your baby’s movement patterns after bleeding begins.
• Fetal heart rate changes noted on a home Doppler or during a prenatal visit.
• History of a velamentous cord insertion, succenturiate lobe, or prior diagnosis of vasa previa.

Even if you feel “fine,” do not wait—vasa previa can cause fetal exsanguination within minutes.<sup>2</sup>

Diagnosis

Because the condition can be fatal for the baby if missed, obstetricians use a combination of screening and targeted imaging:

1. Transvaginal Ultrasound with Color Doppler

This is the gold‑standard test. A skilled sonographer evaluates the cervical os for any vessels that cross over it. Color Doppler highlights blood flow direction, confirming that the vessels are fetal (pulsatile with the fetal heart rate) rather than maternal.

2. Transabdominal Ultrasound (Screening)

Routine third‑trimester scans may incidentally detect low-lying placentas, bilobed placentas, or velamentous insertion, prompting a more detailed transvaginal study.

3. MRI (Rarely Used)

Magnetic resonance imaging can be helpful in complex cases where ultrasound views are limited, but it is not routine.

4. Intrapartum Fetal Monitoring

If vasa previa is suspected during labor, continuous electronic fetal monitoring (EFM) is started immediately. Sudden FHR decelerations in the presence of bleeding strongly suggest fetal vessel rupture.

5. Laboratory Tests

Maternal labs (CBC, blood type, Rh factor) are ordered to prepare for potential maternal transfusion if large‑volume bleeding occurs, but they do not diagnose vasa previa.

Treatment Options

Management centers on preventing vessel rupture and, if rupture occurs, delivering the baby quickly enough to prevent irreversible hypoxia.

1. Planned Cesarean Delivery

When vasa previa is diagnosed antenatally, the standard of care is a scheduled Cesarean section at 34‑36 weeks gestation, before spontaneous labor or membrane rupture. This timing balances fetal lung maturity with the risk of bleeding.<sup>3</sup>

2. Hospital Admission & Close Surveillance

For women with risk factors but no confirmed vasa previa, many clinicians admit them at 32‑34 weeks for twice‑daily non‑stress tests (NST) and ultrasound checks.

3. Steroid Administration

Antenatal corticosteroids (betamethasone 12 mg IM, two doses 24 h apart) are given between 24‑34 weeks to accelerate fetal lung maturity in case an early delivery becomes necessary.

4. Immediate Delivery After Bleeding

If a patient presents with bleeding and confirmed vasa previa, the obstetric team proceeds to an emergency Cesarean within minutes. Rapid transfer to a facility with neonatal intensive care (NICU) is essential.

5. Blood Products & Neonatal Resuscitation

• Maternal IV access for possible transfusion.
• Prepared neonatal team for immediate resuscitation, potential transfusion, and management of anemia.

6. Post‑delivery Follow‑up

Both mother and infant need monitoring for anemia, infection, and placental pathology review to confirm the diagnosis and guide counseling for future pregnancies.

Prevention Tips

While you cannot change the way a placenta forms, several strategies can reduce the risk of vasa previa or lead to earlier detection:

• Early ultrasound screening (around 12‑14 weeks) for cord insertion and placental morphology, especially if you have risk factors (multiple gestation, ART, prior placenta problems).
• Tell your provider about any prior diagnosis of velamentous insertion or succenturiate lobe.
• Avoid smoking and illicit drug use. Both are linked to abnormal placental development.
• Maintain a healthy weight and manage chronic conditions (diabetes, hypertension) before conception.
• Follow-up all recommended third‑trimester scans. If a low‑lying placenta or bilobed placenta is found, request a targeted Doppler study.
• Promptly report any vaginal bleeding, fluid loss, or change in fetal movement.
• Consider delivery at a tertiary center** if you have known risk factors, ensuring immediate access to NICU and surgical teams.

Emergency Warning Signs

If you experience any of the following, call emergency services (911 in the U.S.) or go to the nearest labor and delivery unit immediately:

• Sudden, bright red vaginal bleeding after the membranes have ruptured.
• Bleeding that increases in volume rapidly (more than a few teaspoons).
• Fetal heart rate abnormalities (bradycardia, late decelerations, loss of variability) detected on a fetal monitor or bedside Doppler.
• Severe abdominal pain accompanied by bleeding (could indicate concurrent placental abruption).
• Signs of maternal shock (dizziness, faintness, rapid pulse, pale skin) – rare but possible if a large volume of fetal blood returns to the mother.

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**If you have known risk factors, discuss a birth plan with your obstetrician well before 34 weeks gestation.

References

1. Mayo Clinic. Vasa previa. 2023. https://www.mayoclinic.org
2. American College of Obstetricians and Gynecologists (ACOG). Practice Bulletin No. 226: Placenta Accreta Spectrum. 2022.
3. Cleveland Clinic. Vasa Previa: Diagnosis and Management. 2022. https://my.clevelandclinic.org
4. National Institute of Child Health and Human Development (NICHD). Umbilical Cord Abnormalities. 2021.
5. World Health Organization. WHO Recommendations for Antenatal Care for a Positive Pregnancy Experience. 2022.

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