Impact of biometric measurement error on identification of small‐ and large‐for‐gestational‐age fetuses

Abstract

CONTRIBUTION What are the novel findings of this work?This study examines the impact of measurement errors in fetal head circumference, abdominal circumference and femur length on sonographic estimated fetal weight (EFW) and their effect on the prediction of small-(SGA) and large-(LGA) for-gestational-age fetuses.What are the clinical implications of this work? Measurement error in fetal biometry causes substantial error in EFW, resulting in misclassification of SGA and LGA fetuses. The extent to which improvement can be achieved through effective quality assurance remains to be seen but, as a first step, it is important for practitioners to understand how biometric measurement error impacts on the prediction of SGA and LGA fetuses. ABSTRACTObjectives First, to obtain measurement-error models for biometric measurements of fetal abdominal circumference (AC), head circumference (HC) and femur length (FL), and, second, to examine the impact of biometric measurement error on sonographic estimated fetal weight (EFW) and its effect on the prediction of small-(SGA) and large-(LGA) for-gestational-age fetuses with EFW < 10 th and > 90 th percentile, respectively.Methods Measurement error standard deviations for fetal AC, HC and FL were obtained from a previous large study on fetal biometry utilizing a standardized measurement protocol and both qualitative and quantitative quality-control monitoring. Typical combinations of AC, HC and FL that gave EFW on the 10 th and 90 th percentiles were determined. A Monte-Carlo simulation study was carried out to examine the effect of measurement error on the classification of fetuses as having EFW above or below the 10 th and 90 th percentiles. ResultsErrors were assumed to follow a Gaussian distribution with a mean of 0 mm and SDs, obtained from a previous well-conducted study, of 6.93 mm for AC, 5.15 mm for HC and 1.38 mm for FL. Assuming errors according to such distributions, when the 10 th and 90 th percentiles are used to screen for SGA and LGA fetuses, respectively, the detection rates would be 78.0% at false-positive rates of 4.7%. If the cut-offs were relaxed to the 30 th and 70 th percentiles, the detection rates would increase to 98.2%, but at false-positive rates of 24.2%. Assuming half of the spread in the error distribution, using the 10 th and 90 th percentiles to screen for SGA and LGA fetuses, respectively, the detection rates would be 86.6% at false-positive rates of 2.3%. If the cut-offs were relaxed to the 15 th and 85 th percentiles, respectively, the detection rates would increase to 97.0% and the false-positive rates would increase to 6.3%.Conclusions Measurement error in fetal biometry causes substantial error in EFW, resulting in misclassification of SGA and LGA fetuses. The extent to which improvement can be achieved through effective quality assurance remains to be seen but, as a first step, it is important for practitioners to understand how biometric measurement error impacts the prediction of SGA and LGA fetuses.

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

“…Classification of growth disorders is also affected by errors in biometric measurements in EFW assessment 31 . The consequence of these measurement errors can also be seen on a percentile chart; the position of a measurement on a percentile chart is shifted horizontally by errors in gestational age that originate from errors in CRL.…”

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

“…Previous studies have demonstrated that large systematic differences of mean NT or NT scatter can significantly influence the SPR of individual sonographers 6 . Using theoretical modelling it was recently demonstrated that measurement variation in HC, FL, and AC could cause similar error in EFW and consequent misclassification of SGA and LGA fetuses 15 . We tested this approach within an established service offering universal ultrasound for SGA detection.…”

Caveats in the monitoring of fetal growth using ultrasound estimated fetal weight

“…27 Wright et al concluded that errors in individual fetal measurement cause substantial errors in EFW, resulting in misclassification of small and large-for-gestational ages fetuses. 28 In interpreting EFW measurements in the context of fetal growth, it is important to understand and acknowledge these errors since many obstetric decisions such as timing and mode of delivery are based on EFW. Figure 1 shows that EFW centiles on the INTERGROWTH-21st chart are lower than those on the Hadlock et al, WHO and FMF charts.…”