Learning objectives
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Define vasa previa.
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Describe risks of vasa previa.
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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 ).
Risk Factors
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Use of assisted reproductive technologies
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Second-trimester low-lying placenta/placenta previa (even if resolved)
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Bilobed or succenturiate lobe placentas in the lower uterine segment
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Velamentous cord insertion
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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
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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.
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The placenta is often low-lying, bilobed, or succenturiate
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Physical exam findings
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Very rarely, pulsating vessels in the membranes overlying the cervical os can be palpated
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Clinical findings
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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
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Laboratory testing
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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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Differential Diagnosis
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Funic presentation: A loop of umbilical cord overlying the cervical os
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Cervico—uterine vessels
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Amniotic band or chorioamniotic separation
Management
Antenatal
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Consider betamethasone between 28 and 32 weeks of gestation due to increased risk of emergent preterm delivery
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Consider hospital admission between 30 and 34 weeks of gestation with NST 2–3 times daily
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Emergency cesarean delivery should be performed promptly if cord compression or early labor is detected, ideally before rupture of membranes
Delivery
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Delivery via cesarean delivery is recommended between 34 and 37 weeks of gestation
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Earlier delivery by emergency cesarean delivery is indicated in case of:
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Labor
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Rupture of membranes
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Repetitive variable decelerations
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Vaginal bleeding with fetal surveillance changes such as fetal tachycardia, sinusoidal heart rate pattern, or evidence of pure fetal blood by Apt test or Kleihauer–Betke assessment
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The hysterotomy should avoid aberrant blood vessels. If a fetal vessel is lacerated during delivery, the cord should be clamped immediately to prevent fetal/neonatal blood loss
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Type O negative blood should be available for emergency transfusion of a severely anemic newborn
Vasa Previa Simulation
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