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Vasa Previa – A Complete Patient Guide

Overview

Vasa previa is a rare but serious 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, these vessels can tear, leading to rapid fetal blood loss and, if not managed promptly, fetal death.

Who it affects: The condition occurs only in pregnancy and therefore affects pregnant people and their unborn babies. It is most often diagnosed in the second or early third trimester.

Prevalence: Vasa previa is estimated to occur in 1 in 2,500 to 1 in 5,000 pregnancies worldwide, accounting for roughly 0.02–0.04 % of all births <sup>1</sup>. With routine ultrasound screening, detection rates have risen, improving outcomes dramatically.

Symptoms

Many women with vasa previa have no symptoms until labor begins. However, some may notice warning signs earlier. The following list includes both classic and less‑common presentations:

• Painless vaginal bleeding after membrane rupture (often described as “bloody show”). The blood is fetal‑origin (bright red) and may be profuse.
• Rapid fetal heart‑rate deceleration or loss of variability shortly after membranes rupture.
• Fetal bradycardia (heart rate < 110 bpm) within minutes of rupture.
• Abnormal fetal movement patterns reported by the mother (e.g., sudden decrease in kicks).
• Uterine irritability or frequent contractions that do not correspond with labor progress.
• Maternal abdominal pain is uncommon; pain usually indicates another problem (e.g., placental abruption).

Because the bleeding originates from fetal vessels, the mother may not feel significant blood loss, making fetal monitoring essential.

Causes and Risk Factors

Vasa previa is not caused by a single “thing”; rather, it results from abnormal placental and cord attachment. Key mechanisms include:

• Velamentous cord insertion: The umbilical cord inserts into the fetal membranes rather than directly on the placental disc, leaving vessels exposed.
• Membranous fetal vessels crossing the internal os (true vasa previa) – often seen when the fetus is “velamentous” and the vessels travel over the os.
• Succenturiate or accessory placental lobes: An extra placental lobe connected to the main placenta by fetal vessels that cross the cervix.

Risk Factors

• Prior diagnosis of velamentous cord insertion or vasa previa in a previous pregnancy.
• Multiple gestation (twins, triplets) – risk increases 2–3‑fold.
• Assisted reproductive technologies (IVF, ICSI) – higher incidence of abnormal placentation.
• Low‑lying placenta or placenta previa.
• History of uterine surgery (e.g., myomectomy, previous C‑section) that may affect placental positioning.
• Smoking during pregnancy – associated with abnormal cord insertion.

While these factors raise suspicion, many cases occur without an identifiable risk, underscoring the importance of routine anatomic ultrasound screening.

Diagnosis

Early detection is essential. Diagnosis relies on high‑resolution ultrasound, often complemented by Doppler studies.

Screening Ultrasound (18–22 weeks)

• Transabdominal gray‑scale ultrasound assesses placental location, cord insertion, and any accessory lobes.
• Color Doppler maps fetal vessels; if vessels are seen crossing or near the internal cervical os, a diagnosis of vasa previa is made.

Targeted Second‑Trimester Transvaginal Ultrasound

In high‑risk pregnancies (e.g., known velamentous insertion), a transvaginal approach offers clearer visualization of vessels adjacent to the os.

Late‑Pregnancy Confirmation (30–34 weeks)

Because fetal vessels can shift as the uterus expands, a repeat scan near term confirms persistent vasa previa or rules it out.

Additional Tests

• Fetal non‑stress test (NST) or biophysical profile (BPP): Baseline fetal well‑being assessment.
• Maternal blood typing and antibody screen: In case emergent delivery is needed.

Diagnosis is almost always made via imaging; there is no blood test or genetic marker for vasa previa.

Treatment Options

Management aims to prevent vessel rupture and ensure safe delivery.

Expectant Management with Hospital Observation

• Planned cesarean delivery at 34–37 weeks gestation (often 36 weeks) before spontaneous labor or membrane rupture.
• If premature rupture of membranes (PROM) occurs, immediate hospitalization, maternal‑fetal monitoring, and emergent cesarean are indicated.

Medication

• Corticosteroids (betamethasone 12 mg IM ×2 doses 24 h apart) administered when delivery before 34 weeks is anticipated to accelerate fetal lung maturity.
• Antibiotics may be given prophylactically if PROM occurs to reduce infection risk.

Procedural Interventions

• In‑hospital bedside monitoring with continuous fetal heart‑rate tracing.
• Rapid‑response cesarean section if bleeding or fetal heart‑rate abnormalities develop.

Lifestyle and Activity Modifications

• Limit strenuous activity and heavy lifting after 28 weeks.
• Avoid sexual intercourse after 34 weeks or sooner if advised by a provider (risk of membrane rupture).
• Stay well‑hydrated and maintain balanced nutrition to support overall pregnancy health.

Living with Vasa Previa

While the diagnosis can feel overwhelming, most women deliver healthy babies when the condition is recognized early and managed according to guidelines.

Daily Management Tips

• Attend all prenatal appointments, especially ultrasound visits.
• Keep a pregnancy journal noting any vaginal bleeding, fluid loss, or changes in fetal movement.
• Maintain a list of emergency contacts (obstetrician, nearest hospital with obstetric services, partner).
• Pack a hospital bag by 32 weeks, including copies of ultrasound images showing the vasa previa.
• Consider a birth plan that outlines the timing of scheduled cesarean, preferred hospital, and anesthesia preferences.
• Practice relaxation techniques (deep breathing, guided imagery) to reduce anxiety while awaiting delivery.

Emotional Support

Join a support group (online or in‑person) for parents with high‑risk pregnancies. A mental‑health professional can help manage stress and fear of preterm delivery.

Prevention

Because vasa previa results from abnormal placental development, true primary prevention is limited. However, some measures may lower the overall risk of abnormal cord insertion:

• Quit smoking before or early in pregnancy.
• Maintain a healthy weight and manage chronic conditions (e.g., hypertension, diabetes).
• Discuss any prior placental or cord abnormalities with your obstetrician before conceiving again.
• When using assisted reproductive technologies, discuss techniques that may reduce abnormal implantation (e.g., single‑embryo transfer).

Even with preventive steps, routine ultrasound screening remains the cornerstone of early detection.

Complications

If vasa previa ruptures, the fetus can lose a large proportion of its blood volume within minutes, leading to:

• Fetal hypovolemia and severe anemia.
• Fetal bradycardia and possible cardiac arrest.
• Neonatal neurological impairment (hypoxic‑ischemic encephalopathy) due to inadequate oxygen delivery.
• Preterm birth complications (respiratory distress syndrome, intraventricular hemorrhage).
• In the worst scenario, intrauterine fetal demise.

Prompt cesarean delivery before membrane rupture virtually eliminates these risks. According to the WHO, perinatal mortality for diagnosed and managed vasa previa drops from >40 % (undetected) to <5 % when delivered by planned cesarean at 35–36 weeks <sup>2</sup>.

When to Seek Emergency Care

References

1. Mayo Clinic. Vasa Previa – Symptoms & Causes. Accessed April 2026.
2. Centers for Disease Control and Prevention (CDC). Vasa Previa Fact Sheet. Updated 2023.
3. American College of Obstetricians and Gynecologists (ACOG). Practice Bulletin No. 226: Vasa Previa. 2020.
4. World Health Organization. WHO Maternal Health Guidelines. 2022.
5. Cleveland Clinic. Vasa Previa Overview. Reviewed 2024.

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