Performance of a First-Trimester Early Anatomy Ultrasound Clinic in a High-Risk Population: A Two-Year Implementation Report

BACKGROUND: The standard fetal anatomic survey is performed by ultrasonography between 18 and 22 weeks of gestational age. Advances in ultrasonography technology have driven a move toward early anatomy surveys performed between 11 and 14 weeks. At this gestation, detection rates for fetal anomalies range from 20% to 80%. Earlier detection offers opportunities for genetic screening, informed counselling, and earlier decision-making regarding possible pregnancy interventions. OBJECTIVES: We evaluated the performance of a newly established first-trimester early anatomy ultrasound clinic at a tertiary care centre serving high-risk patients, characterizing completion rates and diagnostic accuracy during its first two years of operation. STUDY DESIGN: Retrospective cohort study of all pregnant individuals who underwent a first-trimester anatomy scan between 11+0 and 14+6 weeks of gestation at a tertiary center between September 2020 and December 2022. Primary outcomes were completion rate and diagnostic accuracy compared with routine second-trimester anatomy scan results. RESULTS: A total of 184 first-trimester anatomy scans were performed. Complete anatomical survey was achieved in 90 scans (48.9%). The most commonly non-visualized structures were the nose and lips (22.8%), cardiac structures (15.8%), and spine (14.1%). Including a case of termination of pregnancy based on early anatomy findings, the prevalence of fetal anomalies was 4.9%. Sensitivity for anomaly detection was 62.5% (95% CI: 30.6-86.3%); specificity was 98.0% (95% CI: 94.2-99.3%); positive predictive value was 62.5% (95% CI: 30.6-86.3%); negative predictive value was 98.0% (95% CI: 94.2-99.3%). The false positive rate was 2.0%. Among cases with missed anomalies, none were attributable to non-visualized structures on early anatomy. CONCLUSIONS: Approximately half of high-risk patients achieved a complete first-trimester anatomical survey at our clinic. Detection sensitivity was 62.5% with a low false positive rate, and missed anomalies on routine anatomy were not related to incomplete visualization on early anatomy. These findings support early anatomy ultrasound as a complementary tool to routine mid-trimester anatomical survey in high-risk populations. TWEETABLE ABSTRACT: First-trimester early anatomy ultrasound achieved 62.5% sensitivity and 98.0% specificity in a high-risk Canadian cohort, with missed anomalies unrelated to incomplete visualization. #MFM #PrenatalDiagnosis #FirstTrimester.