Implementation and Performance of First-Trimester Referral Ultrasound Scan Following the Introduction of National Guidelines

BACKGROUND:To report the implementation across Fetal Medicine units and the agreement between first and second trimester referral scans in the identification of fetal anomalies in cases referred for the expert assessment of the fetal anatomy in the first trimester following the publication of the national guidelines in Italy. METHODS:This multicenter, retrospective study aimed to evaluate the implementation and diagnostic performance of first-trimester referral ultrasound (US) in identifying fetal anomalies, following the introduction of national guidelines in Italy. The analysis included singleton pregnancies referred to nine specialized Fetal Medicine centers between 11+0 and 13+6 weeks' gestation due to increased risk for structural anomalies. Risk was defined as either a nuchal translucency (NT) measurement ≥ 3.5 mm or suspicion of a structural anomaly at initial screening. Only cases undergoing referral US within the specified gestational window were included. Diagnostic accuracy was assessed by comparing findings from first-trimester referral US with those from follow-up referral US performed either at 14-16 weeks or at 19-21 weeks. RESULTS:Out of 344 referred cases, 322 (93.6%) underwent first-trimester referral US within the appropriate timeframe. After excluding miscarriages and terminations, 136 cases were evaluated again at 19-21 weeks and 207 at 14-16 weeks. The agreement between the 11+0-13+6 week and 19-21 week scans was 85.3%, with a sensitivity of 82.0%, specificity of 88.0%, positive predictive value (PPV) of 84.7%, and negative predictive value (NPV) of 85.7%. Agreement between the early and 14-16 week scans was 91.3%, with sensitivity, specificity, PPV, and NPV of 90.7%, 92.1%, 93.9%, and 88.2%, respectively. CONCLUSION:The study demonstrates successful implementation of national first-trimester referral US guidelines in Italy. When performed by experienced operators using a standardized protocol, first-trimester anatomy assessment is feasible and provides high diagnostic accuracy, enabling early detection of structural fetal anomalies.