Vasa previa: screening and ultrasound criteria for prenatal diagnosis of umbilical cord vessel presentation

Vasa previa is characterized by the passage of fetal vessels in the membranes over the internal cervical os or in close proximity to it, without protection by umbilical cord or placental tissue. Rupture of such vessels is associated with high risk to the fetus; therefore, prenatal ultrasound diagnosis is critically important.

Screening and Risk Factors

According to ISUOG Practice Guidelines (performance of third-trimester obstetric ultrasound scan, 2024), in a systematic review of 325 cases of vasa previa, 83% had one or more identifiable risk factors. These include:

• placenta previa;
• bilobed placenta;
• succenturiate placental lobe;
• velamentous insertion of the cord;
• assisted conception.

The presence of these factors supports more focused ultrasound assessment in appropriate women where feasible (ISUOG, 2024).

Ultrasound Methodology for Diagnosis

The accuracy of ultrasound in the diagnosis of vasa previa was evaluated in a systematic review (Ruiter L et al., Ultrasound Obstet Gynecol 2015;45:516-522). Prenatal sonographic diagnosis includes transvaginal scanning with color Doppler mapping; three-dimensional sonographic diagnosis of vasa previa has also been described (Oyelese Y et al., Ultrasound Obstet Gynecol 2004;24:211-215). Specific Doppler velocity thresholds are not provided in the source fragments [to be clarified].

Guidelines

Diagnosis and management are regulated by Green-top guideline No. 27b (Jauniaux ERM et al., BJOG 2019;126:e49-e61). The question of second-trimester screening was reviewed by the UK National Screening Committee (Screening for Vasa Praevia in the Second Trimester of Pregnancy, UK NSC, 2017).