SMFM Consult Series #37: Diagnosis and management of vasa previa

Vasa previa occurs when unprotected fetal blood vessels run through the amniotic membranes and traverse the cervix. Complications include fetal hemorrhage, exsanguination, or death. Diagnosis by ultrasound. Management: antenatal corticosteroids 28-32 weeks, considerations for preterm hospitalization at 30-34 weeks, and delivery at 34-37 weeks of gestation.

Definition: Vasa previa is defined when unprotected umbilical vessels run through the amniotic membranes, and pass over the cervix.

Two types:

• Type I: Velamentous cord insertion and fetal vessels that run freely within the amniotic membranes overlying the cervix or in close proximity of it (2cm from os). (Pregnancies with Low lying placentas or resolved placenta previas are at risk). 
• Type II: Succenturiate lobe or multilobe placenta (bilobed) and fetal vessels connecting both lobes course over or in close proximity of cervix (2cm from os).

Diagnosis:

• Routine ultrasound evaluation of lower uterine segment and placenta
• Detection rate 93% and specificity 99%
• Often made 18-26 weeks of gestation
• If diagnosed in the second trimester, 20% will be resolved
• Placental location and the relationship between the placenta and internal cervical os should be evaluated
• Placental cord insertion site be documented when technically possible

Epidemiology/Incidence: 1/2500 deliveries; perinatal mortality rate for pregnancies complicated by vasa previa < 10%

Risk factors/associations: 

• Velamentous cord insertion
• Succenturiate placental lobe/bilobed placenta
• 60% have history of low lying placenta or second trimester placenta previa
• In vitro fertilization (increases Type I Vasa previa to 1/250)
• Complications: include fetal hemorrhage, exsanguination, or death

Management: 

• Preconception counseling: Goal to prolong the pregnancy safely but in the same time to avoid complications that occur if in labor or with rupture of membranes

Screening/Work-up: Mid trimester fetal anatomy ultrasound

Prenatal care: Reasonable to consider antenatal corticosteroids at  28-32 weeks of gestation in case the need for emergent delivery. Decision for prophylactic hospitalization should be individualized and based on: presence or absence of symptoms (eg, preterm contractions, vaginal bleeding); history of spontaneous preterm birth; logistics (distance from hospital); balancing of the risks that are associated with bedrest and activity restriction.

Delivery: 

• Goal to deliver before rupture of membranes while minimizing the impact of iatrogenic prematurity
• Based on available data, planned cesarean delivery for a prenatal diagnosis of vasa previa at 34-37 weeks of gestation is reasonable
• Viable gestational age with PPROM: cesarean delivery is recommended
• Vasa previa should be suspected when vaginal bleeding is accompanied with sinusoidal pattern in FHT tracing
• Delivery should occur at center capable to provide immediate neonatal transfusion
• Negative blood should be available in case of severe anemic neonate