The impact of individual sonographer variation on the detection of small for gestational age fetuses using a third trimester growth scan.

Abstract

Detection of small for gestational age (SGA) fetuses in a third trimester ultrasound could be affected by variation in sonographer performance. Retrospective analysis of all singleton, non-anomalous ultrasound examinations between 35+0 -36+6 weeks gestation, in a single institution where a universal 36-week scan is offered. Screen positive was defined as estimated fetal weight (EFW) <10th centile; SGA was birthweight <10th centile. Individual sonographers' distributions of head circumference (HC), abdominal circumference (AC) and femur length (FL) were used to assess sonographers' screen positive rate (SPR), detection rate (DR) and true positive rate (TPR). Univariate and multivariate regression analysis was performed to assess the association between the sonographers' mean and SD (SD) for HC, AC, FL and their SPR, DR and TPR. There were 27 sonographers performing more than 50 examinations per year, a total of 5691 scans. The mean incidence of SGA was 10.0%. For an overall SPR of 9.4%, the overall DR was 43.8% (95% CI: 39.6% - 48.1%) and the overall TPR was 46.5% (95% CI: 42.9% - 50.2%). Higher AC scatter (SD difference up to 11.6 mm) was associated with higher SPR (P = 0.001). Lower mean FL (difference up to 3.6 mm) was associated with higher SPR (P = 0.003) and higher DR (P = 0.002). As a result, DR varied amongst different sonographers between 14.3% and 85.7% and TPR varied between 8.3% and 100.0%. Monitoring of individual AC and FL distributions is a simple and effective tool for institutional quality assurance.