Ultrasound estimation of fetal weight accuracy in a regional hospital: A retrospective audit

Abstract

Introduction: Ultrasound estimated fetal weight (EFW) is a vital part of prenatal care.We aimed to determine the accuracy of sonographic EFW at a regional Australian hospital, explore factors associated with EFW accuracy and review accuracy calculation methods.Methods: Ultrasound EFW (Hadlock C) was calculated within one week of a live delivery, for 357 singleton pregnancies. EFW accuracy, the difference between EFW, and live birthweight (LBW), were quantified using percentage error (PE); absolute error (AE); 'signed' error and AE ≤10% of LBW.Results: Estimations of accuracy varied by calculation method, with PE smaller (mean 2.3% [CI 1.5, 3.1], median PE 2.4% [IQR À3.4, 6.7]) than AE (mean 6.4% [CI 5.9, 6.9], median AE 5.1% [IQR 2.7, 9.0]). Signed error indicated the majority of EFWs were overestimates and 80.1% of EFW calculations had an AE within 10% of LBW. EFW inaccuracy (AE ≥10% of LBW) varied between sonographers (p = .023) and scan to delivery interval (p = .003).Conclusions: EFW accuracy rates at the regional hospital were similar to published error rates. EFW accuracy varied with sonographer and with time from scan to delivery. Absolute error provides more useful and comparable information than percentage error of EFW.