P21.09: Incorporation of vasa previa screening into a routine anomaly scan

Abstract

Vasa previa (VP) has a reported fetal mortality of 60% if not recognised before attempt at vaginal delivery. Prenatal detection by ultrasound is possible in nearly all cases, but can be notoriously difficult unless there is a high index of suspicion. We report our experience in detection of VP using a structured protocol as part of the routine fetal anomaly scan at 20-22 weeks. Patients attending anomaly screening at a single centre over a 5 year period (2012-2016) underwent assessment for VP using a structured protocol as a part of a routine fetal anatomy scan. Suspected cases of VP were then re-scanned by a specialist sonographer and subsequently followed up. The diagnosis of VP was assigned by documentation of fetal vessels beneath the membranes, within 20 mm of the internal cervical os. 24690 anatomy scans were performed during the study period and 56 of these were identified as potential VP at the 20 -22 week anomaly scan. Of these, 20 were confirmed by the ultrasound specialist at 28 weeks or later. In five patients the only risk factor was a velamentous insertion. All 20 patients had planned Caesarean delivery but one patient bled at 35 weeks before planned delivery and this fetus died. Another patient experienced bleeding and an emergency Caesarean delivery at 31 weeks 3 days, and this baby lived. The remaining 18 had Caesarean delivery as planned. Placental histology was available in 11 cases. No case of VP was unexpectedly found at delivery during the study period (100% detection). The incidence of vasa previa in this unselected population is 1:1234. Use of a specific protocol as part of routine screening, permits high detection rate (100%), resulting in a low (5%) fetal mortality. We suggest that assessment for VP should be incorporated into routine fetal anatomy screening at 20-22 weeks using a structured protocol similar to one presented here.