• Who it affects: All pregnant people can develop vasa praevia, but the risk is higher in women with certain placental abnormalities or multiple gestations.
• Prevalence: Approximately 1 in 2,500–5,000 pregnancies (0.02–0.04%). Incidence has risen to about 1:2,400 in centers that screen routinely with transvaginal ultrasound (Mayo Clinic, 2023).
• Why it matters: Untreated vasa praevia carries a fetal mortality rate of 20–60% (CDC, 2022). Early detection and planned delivery dramatically improve outcomes, with survival rates >95% when managed appropriately.

Symptoms

Vasa praevia itself rarely produces symptoms before labor; most cases are identified by ultrasound. However, certain warning signs can appear during pregnancy or labor:

• Painless vaginal bleeding after membrane rupture (often described as “large gush” of bright red blood).
• Fetal distress signs on monitoring (e.g., sudden bradycardia, variable decelerations) after rupture of membranes.
• Rapid fetal heart‑rate drop within minutes of membrane rupture.
• Absence of fetal movement shortly after bleeding begins.
• Uterine contractions without cervical change – can indicate hidden blood loss.

Because the condition is often silent until labor, routine screening in at‑risk pregnancies is the key to prevention.

Causes and Risk Factors

Vasa praevia is caused by abnormal positioning of fetal vessels that lie unsupported over the cervical os. The underlying placental or membrane anomalies that create this situation include:

• Velamentous cord insertion – the umbilical cord inserts into the fetal membranes instead of the placental disc, leaving vessels exposed.
• Succenturiate or accessory lobes – extra placental tissue connected by fetal vessels that may cross the os.
• Multifetal pregnancies – twins or higher-order multiples increase the likelihood of velamentous insertion.
• In vitro fertilization (IVF) and other assisted reproductive technologies (ART) – studies show a 2–3‑fold higher incidence (NIH, 2021).
• Low‑lying placenta or placenta previa – abnormal placental placement can pull vessels near the cervical opening.
• Previous uterine surgery (e.g., myomectomy, cesarean scar) – may alter placental implantation patterns.

Who is at highest risk? Women with any of the above placental abnormalities, those who have had a prior diagnosis of velamentous insertion, and patients undergoing IVF/ICSI should be offered targeted ultrasound screening between 18–22 weeks gestation.

Diagnosis

Early detection relies on high‑resolution ultrasound, often combined with Doppler flow studies.

Ultrasound Screening

• Transvaginal ultrasound (TVUS) at 18–22 weeks – the gold‑standard method. The sonographer visualizes the fetal vessels over the internal os and assesses whether they are “protected” by cord tissue.
• Color Doppler – highlights blood flow within the vessels, confirming that they are fetal (as opposed to maternal) and showing their relationship to the cervical opening.
• Three‑dimensional (3D) ultrasound – can give a more detailed map, especially useful when multiple vessels are present.

Follow‑up Imaging

If vasa praevia is detected, a repeat scan at 28–32 weeks verifies that the vessels remain over the os and helps plan delivery timing.

Other Tests

• Fetal non‑stress test (NST) or biophysical profile (BPP) – baseline assessment of fetal well‑being; not diagnostic for vasa praevia but useful for monitoring.
• Maternal serum markers – not diagnostic; however, low‑lying placenta on routine anatomy scan may trigger a targeted vasa praevia screen.

Treatment Options

Management focuses on preventing vessel rupture and ensuring a safe, pre‑term delivery under controlled conditions.

Expectant Management (When Diagnosis is Early & No Bleeding)

• Hospital observation from 30–32 weeks gestation, with twice‑daily fetal heart‑rate monitoring.
• Corticosteroids (e.g., betamethasone 12 mg IM 24 h apart) between 24–34 weeks to promote fetal lung maturity (ACOG, 2022).
• Pelvic rest – avoid intercourse, digital exams, and strenuous activity that could trigger membrane rupture.

Planned Delivery

Most experts recommend a scheduled cesarean section at 35–36 weeks, after confirming fetal lung maturity (often via amniocentesis for surfactant‑protein A) or administering corticosteroids if earlier.

• Cesarean delivery – the preferred route because it avoids cervical dilation and membrane rupture.
• Vaginal delivery – rarely chosen; if undertaken, strict criteria (e.g., no visible vessels over the os, short cervix, immediate access to emergent C‑section) must be met.

Emergent Management (If Bleeding Occurs)

• Immediate bedside fetal monitoring.
• Rapid delivery – most often an emergency cesarean section.
• Neonatal resuscitation with blood transfusion if fetal anemia is suspected.

Lifestyle & Supportive Care

• Hydration & nutrition – maintain adequate maternal weight gain (≈ 25–35 g/kg).
• Stress reduction – relaxation techniques, counseling, or prenatal yoga (as approved by your provider).
• Education – teach the birth partner to recognize warning signs and to call emergency services immediately if bleeding occurs.

Living with Vasa Praevia

Beyond medical appointments, day‑to‑day life can remain normal with a few practical adjustments:

• Scheduled prenatal visits – keep all appointments; most will be every 1–2 weeks after 28 weeks.
• Know your “action plan.” Write down the hospital’s contact number, the name of your obstetric team, and the estimated due date.
• Avoid activities that increase intra‑abdominal pressure – heavy lifting, high‑impact exercise, or straining during bowel movements.
• Travel considerations – If traveling after 30 weeks, stay within 2‑hour reach of a hospital with obstetric capability.
• Prepare for early birth – Pack a hospital bag by 32 weeks, arrange childcare for older children, and discuss parental leave plans.

Prevention

Because vasa praevia stems from placental development, true primary prevention is limited, but risk can be reduced:

• Pre‑conception counseling – discuss IVF techniques that lower velamentous insertion risk (e.g., single‑embryo transfer).
• Early ultrasound screening – requesting a detailed ultrasound at the anatomy scan (19–22 weeks) especially if you have risk factors.
• Optimal management of multiple pregnancies – close monitoring by a high‑risk obstetrician.
• Smoking cessation – smoking is associated with abnormal placentation (CDC, 2022).
• Control of chronic conditions such as hypertension or diabetes, which can affect placental development.

Complications

If vasa praevia goes undiagnosed or is not managed promptly, serious complications can arise:

• Fetal exsanguination – rapid loss of blood leads to hypoxia, acidosis, and death.
• Neonatal anemia – may require blood transfusion and intensive care.
• Preterm birth – emergency delivery often occurs before 34 weeks, increasing risks of respiratory distress syndrome, intraventricular hemorrhage, and long‑term neurodevelopmental issues.
• Maternal complications – while the mother rarely loses blood, she may experience anxiety, prolonged hospitalization, or postpartum hemorrhage unrelated to vasa praevia.
• Psychological impact – fear of sudden bleeding can cause significant stress; counseling or support groups are recommended.

When to Seek Emergency Care

References

1. Mayo Clinic. “Vasa previa.” Updated 2023. https://www.mayoclinic.org/diseases-conditions/vasa-previa
2. American College of Obstetricians and Gynecologists. “Committee Opinion No. 896: Management of Vasa Previa.” 2022.
3. Centers for Disease Control and Prevention. “Maternal and Infant Mortality.” 2022. https://www.cdc.gov/reproductivehealth/maternalinfanthealth/
4. National Institutes of Health. “Assisted Reproductive Technology and Placental Complications.” 2021.
5. Cleveland Clinic. “Velamentous Cord Insertion & Vasa Previa.” 2023. https://my.clevelandclinic.org/health/diseases/21530-velamentous-cord-insertion
6. World Health Organization. “Pre‑term birth.” Fact sheet, 2022.