The impact of ultrasound-based antenatal screening strategies to detect vasa praevia in the United Kingdom: An exploratory study using decision analytic modelling methods

Abstract

The objective of this exploratory modelling study was to estimate the effects of second-trimester, ultrasound-based antenatal detection strategies for vasa praevia (VP) in a hypothetical cohort of pregnant women. For this, a decision-analytic tree model was developed covering four discrete detection pathways/strategies: no screening; screening targeted at women undergoing in-vitro fertilisation (IVF); screening targeted at women with low-lying placentas (LLP); screening targeted at women with velamentous cord insertion (VCI) or a bilobed or succenturiate (BL/S) placenta. Main outcome measures were the number of referrals to transvaginal sonography (TVS), diagnosed and undiagnosed cases of VP, overdetected cases of VCI, and VP-associated perinatal mortality. The greatest number of referrals to TVS occurred in the LLP-based (2,083) and VCI-based screening (1,319) pathways. These two pathways also led to the highest proportions of pregnancies diagnosed with VP (VCI-based screening: 552 [78.9% of all pregnancies]; LLP-based: 371 [53.5%]) and the lowest proportions of VP leading to perinatal death (VCI-based screening: 100 [14.2%]; LLP-based: 196 [28.0%]). In contrast, the IVF-based pathway resulted in 66 TVS referrals, 50 VP diagnoses (7.1% of all VP pregnancies), and 368 (52.6%) VP-associated perinatal deaths which was comparable to the no screening pathway (380 [54.3%]). The VCI-based pathway resulted in the greatest detection of VCI (14,238 [99.1%]), followed by the IVF-based pathway (443 [3.1%]); no VCI detection occurred in the LLP-based or no screening pathways. In conclusion, the model results suggest that a targeted LLP-based approach could detect a substantial proportion of VP cases, while avoiding VCI overdetection and requiring minimal changes to current clinical practice. High-quality data is required to explore the clinical and cost-effectiveness of this and other detection strategies further. This is necessary to provide a robust basis for future discussion about routine screening for VP.

Type III Vasa Previa Associated with Resolution of a Low-Lying Placenta: Case Report and Literature Review

“…3 A recent article comparing different screening strategies found that screening based on low-lying placenta may be superior to screening based on presence of velamentous cord insertion. 8 This case highlights the importance of follow-up ultrasound following a finding of low-lying placenta, and careful assessment of the vessels adjacent to the internal cervical os with TVS color Doppler. In this case, there was an arterial signal at the fetal heart rate, but type III cases with venous vasa previa can occur, making the diagnosis via ultrasound more nuanced.…”

“…It has been suggested that type 3 vasa previa, while currently infrequently reported, may in fact be the most common type of vasa previa 3 . A recent article comparing different screening strategies found that screening based on low lying placenta may be superior to screening based on presence of velamentous cord insertion 8 . This article is protected by copyright.…”

ISUOG Practice Guidelines: performance of third‐trimester obstetric ultrasound scan

“…Third-trimester assessment of the placenta is recommended if there is evidence that the lower placental edge reaches or overlaps the internal cervical os at the time of the routine anomaly scan 10 . Conversely, systematic screening for vasa previa or velamentous cord insertion is not recommended in the third trimester, in view of the technical difficulties and lack of robust evidence regarding its usefulness 31,32 .…”

Vasa Previa

“…However, the UK National Screening Committee continues to recommend not screening for vasa previa. 67 , 71 , 79 , 80 A recent modeling study from the United Kingdom has suggested that targeted screening of all patients with second-trimester placenta previas or low-lying placentas will detect about 60% of cases of vasa previa without leading to increased cost or modification of current protocols. 80 A recent opinion argued that vasa previa is more common than several conditions routinely screened for in pregnancy and, given the high detection rate of ultrasound screening and the dramatic difference in outcomes in prenatally diagnosed cases, advocated that there should be routine screening for vasa previa.…”