The Utility of Repeat Midtrimester Anatomy Ultrasound for Anomaly Detection

Although guidelines recommend repeat ultrasound in the setting of an incomplete fetal anatomic survey, the clinical utility of this practice has not been established. As such, we aimed to assess the yield of repeat ultrasound for anomaly detection following an incomplete survey.

This is a retrospective cohort study of all singletons who underwent a midtrimester anatomic ultrasound at University of Alabama at Birmingham (UAB) from 2006 to 2014. Patients with an incomplete ultrasound underwent repeat examinations until completion. The population was divided into cohorts FIRST, SECOND, and THIRD, corresponding to the ultrasound at which the exam was deemed complete. Each detected anomaly was tallied. The number of ultrasounds needed to detect an anomaly was then assessed per group.

Of 15,768 ultrasounds performed on 13,740 patients, 11,828 exams were completed on first attempt; 1,796 patients required a second, while 116 patients required a third scan or more. We detected 324 anomalies; 93.8% in FIRST, 5.9% in SECOND, and 0.3% in THIRD. The number of scans needed to detect an anomaly was 39, 189, and 348 for FIRST, SECOND, and THIRD, respectively.

Over 90% of anomalies are detected on the initial fetal anatomic survey. The incremental diagnostic yield then decreases, requiring appreciably more repeat scans to detect one anomaly.