Vasa previa screening remains a controversial topic in obstetric imaging, despite the condition’s high risk for fetal mortality. This is the key finding from a new review that assessed national and international obstetric ultrasound guidelines. Consequently, many protocols either completely omit mention of vasa previa (VP) or fail to recommend a structured, evidence-based screening approach. This failure to adopt modern screening strategies may contribute to preventable perinatal deaths.
The Disparity in Vasa Previa Screening Guidelines
Researchers conducted a comprehensive evaluation of 20 national and two international obstetric imaging guidelines. They found that 12 of these mentioned VP, however, none explicitly recommended routine VP screening for all pregnant individuals. Therefore, the current global practice shows a significant lack of consensus on universal screening protocols. In contrast, robust evidence demonstrates that prenatal diagnosis dramatically improves outcomes.
Undiagnosed VP carries a perinatal mortality rate as high as 56%. Nevertheless, a prenatal diagnosis, typically followed by an appropriately timed late preterm Cesarean delivery, reduces this mortality risk to less than 1%. Moreover, this striking difference in outcome strongly suggests that existing guidelines are not keeping pace with clinical evidence.
Essential Strategies for Vasa Previa Detection
The review showed some partial adoption of detection strategies. For instance, nine national guidelines did recommend the routine assessment of the placental cord insertion site. This is a critical step because a velamentous cord insertion is a major risk factor for VP. In contrast, none of the reviewed guidelines endorsed routine color flow Doppler assessment of the lower uterine segment.
Only five national guidelines recommended a third-trimester transvaginal ultrasound with color flow Doppler. They suggested this targeted approach to rule out VP in pregnancies complicated by a second-trimester low-lying placenta or placenta previa. A number of experts, furthermore, now advocate for universal VP screening during the second-trimester anatomy scan. This universal approach can greatly enhance the early identification of at-risk pregnancies.
Vasa Previa Screening and Risk Factors
Only five national societies have developed dedicated VP guidelines. Yet, even these dedicated recommendations sometimes show inconsistencies with recent evidence. For example, some professional bodies cite insufficient evidence or an uncertain balance of benefit versus harm for not recommending routine screening. Consequently, many pregnancies with known risk factors might still be missed under current protocols.
Risk factors like velamentous cord insertion, a low-lying placenta in the second trimester, IVF pregnancies, and multiple gestations necessitate targeted screening. Transvaginal color Doppler ultrasound is the gold standard for diagnosing VP in these high-risk cases. Ultimately, integrating VP detection strategies—like routine cord insertion assessment and targeted transvaginal Doppler—into standard obstetric imaging offers minimal additional resource burden and a significant impact on fetal survival.
Frequently Asked Questions
Q1: What is the main finding of the guideline comparison study?
The study found that while vasa previa (VP) is mentioned in many guidelines, none of the 20 national and two international obstetric imaging guidelines reviewed explicitly recommend routine screening for VP in all pregnant individuals.
Q2: Why is prenatal diagnosis of vasa previa so critical?
Undiagnosed vasa previa is associated with a perinatal mortality rate as high as 56%. However, prenatal diagnosis using ultrasound and colour Doppler, followed by planned late preterm delivery via Cesarean section, reduces this mortality rate to less than 1%.
Q3: Which specific screening strategies are recommended by evidence-based approaches?
Evidence-based strategies strongly recommend the routine assessment of the placental cord insertion site during the second-trimester scan. Additionally, a transvaginal ultrasound with colour flow Doppler should be used to rule out VP in high-risk cases, such as those with a second-trimester low-lying placenta or placenta previa.
References
- Agudogo S et al. Vasa previa screening: comparison of national and international obstetric imaging guidelines. Ultrasound Obstet Gynecol. 2026 Jan 17. doi: 10.1002/uog.70167. PMID: 41546609.
- ISUOG. How to screen for vasa previa.
- NIH. Vasa Previa – PMC.
- Evidence-based Diagnosis and Treatment of Vasa Previa: Clinical Obstetrics and Gynaecology.