Ultrasonographic fetal weight estimation: accuracy of formulas and accuracy of examiners by birth weight from 500 to 5000 g.

Objective: To determine the accuracy of birth weight in different birth weight (BW) groups using widely accepted formulas for fetal weight estimation (EFW). The secondary purpose was to estimate the role of examiners on the accuracy of EFW.

Methods: The cross-sectional data were obtained from 5612 pregnant women. Fetal weight was estimated for each fetus using the formulas of Campbell and Wilkin, Shepard, 2 formulas of Hadlock and Merz. Inclusion criteria were: singleton pregnancy, complete ultrasound parameters, EFW obtained within the last week prior to delivery, the live born infant without congenital malformations or hydrops.

Results: The highest intraclass correlation coefficient and the most stable results in all BW groups were generated with both Hadlock formulas. Both Hadlock and Campbell formulas had the lowest percent errors (PE) in BW groups between <1500 g and 3500 g. Shepard and Merz formulas had lower PEs in BW groups between 3501 g and >4000 g. However in BW groups under 3500 g they were imprecise. The PE of EFW varied from -4.0 +/- 8.5% to 1.3 +/- 8.5% between examiners.

Conclusions: Both Hadlock formulas showed the most stable results in all of the weight groups. There is also a need for routine evaluation of the accuracy of EFW for every examiner, to make suggestions, what fetal measurements must be improved to improve EFW.