Background: Accurately estimated foetal weight (EFW) is critical for obstetric management, yet conventional two-dimensional biometric foetal formulas often exhibit significant error margins due to their failure to account for foetal soft tissues. This study evaluated the reliability of 2-dimensional and 3-dimensional foetal thigh volume measurements as predictors of actual birth weight (ABW) within a Nigerian population. Materials and Methods: This cross-sectional study was conducted among 150 apparently healthy pregnant women (36–40 weeks gestation) at a diagnostic facility in Onitsha, Anambra State. Two-dimensional biometry was performed using the Hadlock IV formula, while three-dimensional thigh volumes were examined using a Mindray (EA6132B) volumetric transducer and analyzed offline via MicroDicom software. Statistical analysis was performed using Pearson’s correlation, linear regression, and Bland-Altman agreement analysis via IBM SPSS version 21.0. Results: The mean ABW was 3.76 ± 0.34 kg, while that of 2-D EFW was 3.63±0.36 kg. A significant positive correlation (p<0.001) was found for both 2-D (r=0.504) (p = < 0.001) and 3-D (r = 0.589) (p = <0.001) thigh volumes against the actual birth weight measured at birth. The Bland-Altman analysis revealed a systematic mean bias of −0.12 kg, confirming that conventional 2-D biometry consistently underestimates birth weight in the study population. High predictive power was observed in the derived 3-D regression model (R2 = 0.977). A novel prediction regression equation (3D ThV=94.947+0.276×2D ThV) was developed to estimate three-dimensional volumes from two-dimensional parameters. Conclusion: Three-dimensional foetal thigh volume is a more reliable predictor of birth weight than two-dimensional measurements, as it more accurately reflects subcutaneous tissue mass. The localized regression models developed in this study provides improved weight prediction and obstetric outcomes in resource-limited settings.