OC192: Ultrasound weight estimation of large fetuses: A comparative study of two‐ and three‐dimensional methods

Abstract

Objectives: To compare two-dimensional (2D) and threedimensional (3D) ultrasound techniques, including volumetry of fetal thigh, for weight estimation of large fetuses, and to develop a new fetal weight (FW) estimation formula. Methods: In a prospective comparative study FW estimation was done on 176 pregnant women at ≥287 days of gestation ≤ 4 days before delivery. Fetal head (BPD or HC), abdomen (AD) and femur were measured with 2D ultrasound technique and the volume of fetal thigh (Tvol) was estimated with 3D technique. The 2D formula of Persson and Weldner (1) was compared with the 3D formula of Lee et al(2). A new formula was developed in a subgroup of 63 fetuses where volumetry of abdomen (Abdvol) was done and the formula (FW = 2088.4904 + 81.0519 × HC − 0.1214 × HC × HC − 69.0966 × AD + 0.4741 × AD × AD + 6.4044 × Tvol + 0.0534 × Abdvol) was tested on another 50 women. Results: Standard deviation (SD) of the mean percent error (MPE) was 6.3% for both the 2D and 3D formulas, and 5.6% for the new formula. Significantly more FW estimated by the 2D formula and the new formula than by the 3D formulas were within both ±5% and ±10% of the birth weight, 50 and 86% (Persson and Weldner), 52 and 86% (new formula), 41 and 73% (Lee), respectively. In the independent Test group the SD of MPE was similar for the 2D, 3D and new formulas, 7.02, 7.04 and 7.09%, respectively. Conclusion: FW of large fetuses was estimated using 2D ultrasound method with same accuracy as with 3D ultrasound. 3D ultrasound technique requires technically advanced and expensive equipment, special operator training and skills, and it is time consuming. At present, to abandon the 2D ultrasound method in favour of 3D ultrasound for FW estimation seems not reasonable.