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Vasa Previa: Diagnosis and Management

Vasa previa is defined as fetal vessels that run through the fetal membranes, over or near the endocervical os (2 cm or less) and are unprotected by placenta or umbilical cord.


Deliver by cesarean section before the onset of labor and before rupture of membranes

  • Scheduled delivery 34w0d to 37w0d
  • Deliver by cesarean section in the case of PPROM and viability
  • Antenatal corticosteroids 28 to 32 weeks gestation
  • SMFM guidance states to consider hospitalization at 30 to 34 weeks
    • Benefit is unproven and there have been good outcomes reported with outpatient management
    • When considering hospitalization, individualize based on the following
      • Symptoms
      • History of preterm birth
      • Logistics in getting to hospital with transfusion capabilities
    • Patients with normal cervical lengths are the best candidates for possible outpatient management
  • Repeat ultrasound in the third trimester is suggested if vasa previa is suspected in the second trimester, as approximately 20% of apparent vasa previa will resolve by the late third trimester


Vasa previa occurs in 1/2500 to 1/5000 pregnancies and is associated with an increased risk of preterm birth and the associated complications of prematurity. There is a 97% survival rate when diagnosed by prenatal ultrasound and a 44% survival rate when the diagnosis is made intrapartum.


  • Risk factors:
    • Velamentous cord insertion (Type 1 vasa previa)
    • Succinturate or bilobed placenta connecting vessels (Type 2 vasa previa)
    • Placenta previa or low lying placenta in the second trimester
    • Multiple gestation
    • IVF (1/250 risk of Type 1 vasa previa)
  • In cases of low lying placenta, bilobed placenta, succinturate placenta or velamentous cord insertion, a targeted ultrasound for vasa previa should be performed
  • Screening possible at 2nd trimester fetal anatomy ultrasound
    • If detected on 2nd trimester ultrasound, 20% will resolve
    • Document cord insertion site if possible
  • Diagnosis is made by ultrasound, ideally with transvaginal and color flow Doppler
  • Ultrasound findings include a linear tubular echolucent body overlying the endocervical os with color flow doppler demonstrating flow through the structure and pulsed doppler showing fetal vascular wave forms
  • Risk of perinatal loss due to fetal exsanguination – watch for sinusoidal pattern on FHT tracing
  • Plan for delivery at a center that can perform neonatal transfusion if required
    • Note: Center should have negative blood available for neonate in case rapid transfusion is necessary

Learn More – Primary Sources:

SMFM: Diagnosis and management of vasa previa

ACOG/SMFM Committee Opinion 831: Medically Indicated Late-Preterm and Early-Term Deliveries

Society for Maternal-Fetal Medicine (SMFM) Consult Series #44: management of bleeding in the late preterm period

Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta

Locate a Maternal Fetal Medicine Specialist:

Maternal-Fetal Medicine Specialist Locator-SMFM

Placenta Previa – Nomenclature, Diagnosis and Clinical Management

Clinical Actions:

The incidence of placenta previa is 1/200 pregnancies. Most cases of placenta previa will be identified prenatally by prenatal ultrasound. The following is recommended regarding mode and timing of delivery

  • Placenta previa: Cesarean delivery only
  • Placenta edge is ≥2.0 cm from the internal cervical os
    • Trial of labor is appropriate
  • Placental edge is between 1.0 cm and 2.0 cm from the internal cervical os
    • Management is uncertain
  • Timing of delivery in stable cases
    • ACOG/SMFM: 36w0d to 37w6d
  • Hospitalize when there are contractions or vaginal bleeding
  • Consider corticosteroids to enhance pulmonary maturity when there is vaginal bleeding <34 weeks gestation
  • The benefits of tocolysis, bed rest, pelvic rest and reduced activity is uncertain


The nomenclature has been modified and the terms partial and marginal have been eliminated. All placentas which overlie or abut the internal cervical os (to any degree) should be referred to as placenta previa. A placenta which is near to but not overlying the os is termed a low-lying placenta.

Key points:

  • Role of ultrasound
    • Transvaginal ultrasound is the recommended approach
    • Transvaginal ultrasound is more accurate than transabdominal approach
    • If placenta previa is suspected on transabdominal ultrasound, a transvaginal ultrasound should be performed
  • Placenta previa identified during second trimester ultrasound
    • Placenta previa may be seen in 1 to 4% of second trimester ultrasound exams
    • 10 to 20% of previas diagnosed at 20 weeks gestation will remain a previa in the late 3rd trimester
    • Repeat ultrasound at 32 weeks gestation
  • The incidence of placenta previa is increased by
    • Number of previous cesarean sections
    • Number of previous spontaneous deliveries
    • the number of elective terminations
    • prior uterine surgery
    • maternal parity
    • maternal age
    • smoking
    • cocaine use
    • multiple gestations
    • prior placenta previa
  • Fetal complications are primarily those associated with prematurity
  • There is an increased risk of postpartum hemorrhage in patient with placenta previa
  • General anesthesia may increase blood loss without improving safety

Learn More – Primary Sources:

Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta

Society for Maternal-Fetal Medicine (SMFM) Consult Series #44: management of bleeding in the late preterm period

The Incidence of Postpartum Hemorrhage in Pregnant Women with Placenta Previa: A Systematic Review and Meta-Analysis

Analysis of first and second trimester maternal serum analytes for the prediction of morbidly adherent placenta requiring hysterectomy