Accuracy of fetal weight estimation at term: comparison of conventional and soft tissue-based ultrasound methods.

OBJECTIVE: To compare the accuracy of conventional two-dimensional (2D) fetal weight estimation models with methods incorporating 2D and three-dimensional (3D) soft tissue measurements at term. STUDY DESIGN: This prospective study included 199 low-risk pregnant women who underwent ultrasound assessment within 10 days prior to delivery at a tertiary hospital in Spain. Estimated fetal weight was calculated using the Hadlock, Lee, and Scioscia formulas, incorporating standard 2D biometric parameters and fractional thigh volume. Estimated fetal weights were compared with actual birth weight using correlation analysis and assessment of systematic and random errors. RESULTS: All models showed a positive correlation with birth weight. The Hadlock formula demonstrated the highest overall correlation (r = 0.68) and the greatest proportion of estimates within 5% of birth weight (42.7%). In fetuses weighing <3000 g, the Lee model showed higher accuracy. CONCLUSION: The Hadlock formula showed the most consistent overall performance for fetal weight estimation at term. Soft tissue-based models may offer limited benefit in smaller fetuses, although their routine use does not appear to improve overall accuracy.