Makindo Medical Notes

Introduction

Vasa praevia is a rare but serious obstetric condition where fetal blood vessels run across or near the internal opening of the cervix, unprotected by the placenta or umbilical cord. These vessels are at high risk of rupture during labor or when the membranes rupture, leading to life-threatening hemorrhage for the fetus.

Incidence

• Vasa praevia occurs in approximately 1 in 2,500 to 5,000 pregnancies.
• Though rare, it carries a high risk of fetal mortality if not diagnosed and managed promptly.

Types of Vasa Praevia

• Type 1: The fetal vessels connect the placenta to a velamentous umbilical cord insertion, running across the cervical os.
• Type 2: The fetal vessels connect to a bilobed or succenturiate-lobed placenta, passing over or near the cervical os.

Risk Factors

• Velamentous cord insertion (where the umbilical cord inserts into the membranes rather than directly into the placenta)
• Placenta previa or low-lying placenta
• Multiple gestation (twins, triplets, etc.)
• In vitro fertilization (IVF)
• Accessory placental lobes (succenturiate lobes)

Clinical Presentation

• Often asymptomatic and undetected before labor if no antenatal screening is performed.
• Vaginal bleeding, especially after the rupture of membranes, which is often painless but involves bright red blood.
• Fetal distress or sudden fetal bradycardia (a drop in fetal heart rate) during labor or upon membrane rupture.

Diagnosis

Early diagnosis through antenatal ultrasound is critical to prevent fetal mortality. Diagnostic methods include:

• Transvaginal Ultrasound with Color Doppler: The most effective method for diagnosing vasa praevia. It allows visualization of the fetal vessels crossing the cervical os.
• Transabdominal Ultrasound: May detect abnormal placental or cord positions but is less accurate than transvaginal ultrasound.
• Palpation of Fetal Vessels: Rarely, fetal vessels may be palpated during a vaginal examination, but this is not a reliable diagnostic method.

Management

Management depends on the timing of diagnosis and the severity of the condition:

• Antenatal Diagnosis (before rupture of membranes):
  • Planned delivery by elective caesarean section around 34-36 weeks is the standard management to avoid labour and rupture of membranes.
  • Hospital admission may be recommended from around 30-32 weeks for close monitoring in case of premature labor.
  • Administer corticosteroids to promote fetal lung maturity if early delivery is anticipated.
• Unrecognized Vasa Praevia (diagnosed during labour):
  • Immediate emergency caesarean section to prevent fetal exsanguination.
  • If the fetal vessels rupture, rapid intervention is required as the fetus may lose a significant volume of blood in minutes.

Complications

• Fetal Mortality: Without antenatal diagnosis and proper management, the fetal mortality rate from vasa praevia can be as high as 50-95%, often due to fetal exsanguination during labour or membrane rupture.
• Fetal Hypoxia: If the fetal vessels are compressed or rupture, the fetus may suffer from oxygen deprivation, leading to long-term neurological damage or stillbirth.

Prognosis

With antenatal diagnosis and appropriate management (including planned caesarean delivery before labor), the prognosis is excellent, with survival rates of over 97%. However, if undiagnosed, the risk of fetal death remains extremely high.

References

• RCOG Green-top Guideline: Vasa Praevia Diagnosis and Management
• Vasa Praevia: A Preventable Tragedy? (NCBI)