Ultrasound Screening for Vasa Previa: A Systematic Review and Meta-Analysis.

OBJECTIVE To evaluate the prenatal detection of vasa previa (VP) 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 VP screening, with third-trimester ultrasound confirmation and verification at delivery, over at least one year. Eligible studies reported both the total number of pregnancies screened and the number of confirmed VP 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 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 1,817 publications, 19 met inclusion criteria, encompassing 779,845 pregnancies and 505 VP cases (1 in 1,544). 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% CI: 0.99-1.00; I2 = 0%), and specificity was also 1.00 (95% CI: 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% CI: 88.30%-100.00%; I2 = 0%). Results remained consistent after excluding studies at high risk of bias. No evidence of publication bias was found. CONCLUSIONS Standardized screening for VP 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 VP.