Key takeaways:
- Standardized second-trimester ultrasound screening with third-trimester confirmation detected 97.8% of vasa previa cases across more than 770,000 pregnancies.
- Screening demonstrated near-perfect diagnostic performance, with pooled sensitivity and specificity of 1.00 and very low false-positive and false-negative rates.
- Prenatal diagnosis of vasa previa was associated with high perinatal survival, with a pooled survival rate of 98.15%.
- Universal screening and targeted screening both showed high detection and survival rates, though data for targeted screening were limited.
- Because up to 20% of vasa previa cases occur without identifiable risk factors, routine screening may reduce missed diagnoses and prevent perinatal deaths.
Vasa previa is a rare but life-threatening obstetric condition, and evidence from a large systematic review indicates that standardized prenatal screening can identify nearly all affected pregnancies and is associated with high perinatal survival.1
Vasa previa occurs when unprotected fetal blood vessels traverse the membranes over or near the cervix.2 Rupture of these vessels during labor or membrane rupture can result in rapid fetal hemorrhage and death.1 Although vasa previa complicates approximately 1 in 1200 pregnancies, undiagnosed cases carry a high risk of stillbirth or neonatal death.
"There is considerable controversy about whether to screen for [vasa previa] prenatally... However, approximately 15% to 20% of cases of VP have no risk factors and thus may be missed by targeted screening," wrote investigators.
Clarifying the value of structured prenatal screening
The objective of this systematic review and meta-analysis was to evaluate the accuracy of standardized second-trimester ultrasound screening for vasa previa, with confirmation in the third trimester, and to estimate perinatal survival in screened populations. Cohort studies were eligible if they implemented a prospective, standardized second-trimester ultrasound screening protocol for vasa previa, either universally or in targeted high-risk populations, with confirmation later in pregnancy.
Standardized screening protocols included routine assessment of placental cord insertion, systematic evaluation of the region overlying the cervix using grayscale ultrasound or color Doppler, transvaginal ultrasound in patients with risk factors, and follow-up imaging for placenta previa or low-lying placenta. Only cases of vasa previa persisting to delivery were included.
Databases searched included MEDLINE, Embase, Web of Science, Global Health, and Global Index Medicus from inception through February 16, 2024. Two independent reviewers performed study selection, data extraction, and risk-of-bias assessment using the QUADAS-2 tool.
Detection accuracy across nearly 780,000 pregnancies
Nineteen cohort studies met inclusion criteria, representing 779,845 screened pregnancies. A total of 505 pregnancies were complicated by vasa previa at delivery, corresponding to an incidence of approximately 1 in 1544. Of these cases, 494 were diagnosed prenatally, yielding a detection rate of 97.8%.
