Ultrasound screening for vasa previa: a systematic review and meta-analysis

Abstract

Objective: To evaluate the prenatal detection of vasa previa and perinatal survival in studies that implemented standardized protocols of prospective second-trimester ultrasound screening protocols followed by ultrasound confirmation in the third trimester.

Data sources: PubMed/MEDLINE, Web of Science, Embase, Global Health, and Global Index Medicus were searched from inception to February 16, 2024.

Study eligibility: We included cohort studies that implemented standardized second-trimester ultrasound protocols-either universal or targeted-for vasa previa screening, with third-trimester ultrasound confirmation and verification at delivery, over at least 1 year. Eligible studies reported both the total number of pregnancies screened and the number of confirmed vasa previa cases. Protocols included assessment of placental cord insertion, cervical region imaging, and transvaginal color Doppler in at-risk patients. We excluded first-trimester-only screening, case reports, reviews, conference abstracts, and overlapping populations.

Study appraisal and synthesis methods: Two reviewers independently screened studies and extracted data, with discrepancies resolved by consensus. Risk of bias was assessed using Quality Assessment of Diagnostic Accuracy Studies, version 2 (QUADAS-2). Meta-analyses of sensitivity, specificity, and perinatal survival were conducted using fixed effects models with inverse-variance weighting using R version 4.4.0 (R Core Team, 2024). Heterogeneity was assessed with chi-square, τ², and I² statistics. Sensitivity analyses excluded studies with high risk of bias. Publication bias was evaluated using funnel plots and Egger's test.

Results: Of 1817 publications, 19 met inclusion criteria, encompassing 779,845 pregnancies and 505 vasa previa cases (1 in 1544). Of these, 494 (97.8%) were diagnosed prenatally. The pooled sensitivity of standardized second-trimester ultrasound screening-with third-trimester confirmation-was 1.00 (95% confidence interval, 0.99-1.00; I²=0%), and specificity was also 1.00 (95% confidence interval: 1.00-1.00; I²=0%), based on 774,937 pregnancies and 11 false positives. Perinatal survival among prenatally diagnosed cases ranged from 87.5% to 100%, with a pooled survival rate of 98.15% (95% confidence interval, 88.30% to 100.00%; I²=0%). Results remained consistent after excluding studies at high risk of bias. No evidence of publication bias was found.

Conclusion: Standardized screening for vasa previa is associated with a high detection rate and high perinatal survival, with minimal false positive and false negative rates. These findings make a strong case for standardized screening for vasa previa.

Keywords: placenta; prenatal diagnosis; prevention; screening; stillbirth; ultrasound; umbilical cord; vasa previa; velamentous cord insertion.