Crown- rump length measurement error: impact on assessment of growth

Objective To examine the impact of first-trimester crown- rump length (CRL) measurement error on the interpretation of estimated fetal weight (EFW) and classification of fetuses as small-, large- or appropriate-for-gestational age on subsequent growth scans. Methods We examined the effects of errors of +/- 2, +/- 3 and +/- 4mm in the measurement of fetal CRL on percentiles of EFW at 20, 32 and 36weeks' gestation and classification as small-, large- or appropriate-for-gestational age. Published data on CRL measurement error were used to determine variation present in practice. Results A measurement error of -2mm in first-trimester CRL shifts an EFW on the 10th percentile at the 20-week scan to around the 20th percentile, and the effect of a CRL measurement error of + 2mm would shift an EFW on the 10th percentile to around the 5th percentile. At 32 weeks, a first-trimester CRL measurement error would shift an EFW on the 10th percentile to the 7th (+ 2 mm) or 14th (-2 mm) percentile; at 36weeks, the EFW would shift from the 10th percentile to the 8th (+ 2 mm) or 12th (-2 mm) percentile. Published data suggest that measurement errors of 2mm or more are common in practice. Conclusion Because of the widespread and potentially severe consequences of CRL measurement errors as small as 2mm on clinical assessment, patient management and research results, there is a need to increase awareness of the impact of CRL measurement error and to reduce measurement error variation through standardization and quality control. (C) 2021 International Society of Ultrasound in Obstetrics and Gynecology.