Detection of vasa praevia in the mid‐trimester ultrasound by Australian sonographers

Abstract

Objective To ascertain Australian obstetric sonographers knowledge and current practice when assessing for vasa praevia in the mid‐trimester ultrasound with the view to improve prenatal diagnosis. Methods Between August and September 2018, a survey was emailed to 4868 Australian sonographers registered to participate in Australian Sonography Association Registry (ASAR) facilitated research projects. A total of 577 responses were received. The sonographers survey response was compared with published Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) recommendations. Results There appears to be an unfamiliarity with the RANZCOG recommendations, in particular that vasa praevia is defined as a fetal vessel lying within 20 mm of the cervical internal os (IOS). Transabdominally, if a vasa praevia risk factor is identified (including a fetal vessel observed in the lower uterine segment), less than 48% of surveyed sonographers proceed to a targeted transvaginal scan. Conclusion To enable effective diagnosis of vasa praevia, it is important to recognise associated risk factors that can raise suspicion for a potential vasa praevia; these are velamentous cord insertion, succenturiate lobe, and low‐lying placenta. A lower threshold of performing a transvaginal ultrasound when risk factors are identified (including a fetal vessel is identified in the lower uterine segment) may significantly improve vasa praevia diagnosis in the mid‐trimester ultrasound.

Vasa praevia diagnosis in the mid trimester ultrasound

“…Vasa praevia has three main risk factors; velamentous cord insertion, succenturiate lobe and a low lying placenta 2,3 . Universal screening of the lower uterine segment with colour Doppler should be performed transabdominally at every mid trimester ultrasound as 17% of vasa praevia cases will have no identifiable risk factors on ultrasound 3,5 . This is achieved by performing a dynamic assessment sweeping the transducer longitudinally and transversely with a colour Doppler box (on appropriate settings) over the lower uterine segment to identify vessels within 20mm of the cervical IOS 2,3,6 …”