Estimation of Fetal Weight: Accuracy of Regression Models versus Accuracy of Ultrasound Data

Abstract

Objectives: To determine the respective importance of equation accuracy and variability in interexaminer measurements in estimation of fetal weight (EFW). Methods: The study included 3 samples from three different French maternity hospitals. Sample 1 (6,508 fetuses) was used to compute a new linear regression model estimating fetal weight (FW) from ultrasound measurements. Sample 2, with 705 fetuses, was used to compare the accuracy of the new equation with Hadlock’s equation. Sample 3 (1,461 fetuses) was used to assess – from our equation and from Hadlock’s – the estimation errors due to the variability of ultrasound measurements recorded by 11 distinct examiners. Accuracy was determined by the signed percent difference (%Diff). Statistical analysis included the F test for correlated variances and comparisons of correlated variances. Results: The random error of our model is 6.8%, significantly lower (p < 0.01) than Hadlock’s which is around 7.4% (8.9% for low FW and 7.4% for high FW). The variability of ultrasound measurements among the different examiners in sample 3 generated a significant variation (p < 0.01) in the random error, ranging from 6.7 to 12.5%. This significant variation was also observed using Hadlock’s equation for the same sample (from 7.2 to 12%). Conclusion: The accuracy of EFW depends much more on the quality of ultrasound measurements than on the choice of equation. Nevertheless, optimizing the accuracy of EFW (about 6.7–6.8%) imperatively requires standardized data collecting.

Accuracy of Sonographic Fetal Weight Estimation within 14 Days of Delivery in a Jordanian Population Using Hadlock Formula 1

“…The fetal head measurements were made in the axial plane at the level where the continuous midline echo is broken by the cavum septum pellucidum in the anterior third. The head circumference was measured around the perimeter using an electronic ellipse as described by Campbell and Thoms [12,13]. The abdominal circumference was measured in the transverse axial view of the fetal abdomen at the level of the liver, identifying the spine and descending aorta posteriorly, the umbilical vein in the anterior third and the stomach bubble in the same plane; just above the level of the cord insertion measurements were taken around the perimeter as described by Campbell et al [7,8].…”