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Vasa Previa


Learning objectives

  • Define vasa previa.

  • Describe risks of vasa previa.

  • Describe antenatal management of vasa previa.

The term vasa previa refers to fetal blood vessels present in the membranes covering or within 2 cm of the internal cervical os . These vessels are not protected by Wharton's jelly and are at risk for rupture upon spontaneous or artificial rupture of the membranes. Their presence can be a result of either velamentous cord insertion or a succenturiate lobe. If fetal bleeding occurs, fetal exsanguination can occur within minutes. These vessels are also at risk of compression from the presenting part, and compression can lead to asphyxia ( Fig. 15.1 ).

Fig. 15.1
Vasa previa. (A) This condition is defined by the fetal blood vessels embedded in the membranes within 2 cm of the internal cervical os. These fetal vessels do not have protective Wharton's jelly. Figure (B) shows placenta after delivery. The arrow indicates fetal vessels that were located above cervical os.

Risk Factors

  • Use of assisted reproductive technologies

  • Second-trimester low-lying placenta/placenta previa (even if resolved)

  • Bilobed or succenturiate lobe placentas in the lower uterine segment

  • Velamentous cord insertion

  • Multiple gestations

Diagnosis

Perinatal mortality is <3% when it is diagnosed antenatally. Mortality rises to nearly 60% when vasa previa is diagnosed intrapartum or postpartum

  • Ultrasound findings

    • Linear sonolucent area crossing over the internal os. Color Doppler flow reveals arterial or venous waveforms ( Fig. 15.2 )

      Fig. 15.2, Ultrasound image showing vasa previa.

      Technical and nontechnical skills for vasa previa.

    • The placenta is often low-lying, bilobed, or succenturiate

  • Physical exam findings

    • Very rarely, pulsating vessels in the membranes overlying the cervical os can be palpated

  • Clinical findings

    • A clinical diagnosis should be suspected when there is vaginal bleeding upon rupture of the membranes with fetal heart rate abnormalities, especially a sinusoidal pattern or bradycardia

  • Laboratory testing

    • The Apt test has been described to differentiate fetal versus maternal bleeding. However, the emergent nature of bleeding vasa previa precludes the clinical utility of this test.

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