A modified model can improve the accuracy of foetal weight estimation by magnetic resonance imaging.

PURPOSE: To determine whether birth weight can be reliably estimated using three-dimensional (3D) magnetic resonance imaging (MRI) foetal body volume at term.

METHOD: Foetuses between 37+5 weeks and 41 weeks of gestation were delivered within 7 days after MRI and ultrasound (US) examinations. 3D foetal models were reconstructed from MRI data, and body volume was calculated. The MRI-based weight estimations were calculated using the Baker equation and the modified Baker equation with a higher density coefficient. The US-based weight estimations were determined using the formula by Hadlock. Estimations based on MRI and US were compared with the birth weights.

RESULTS: Among 22 foetuses that underwent both US and MRI evaluations within 48 h before labour, the mean random errors for the estimated weight based on US, the Baker equation and the modified Baker equation were 6.5%, 4.8%, and 4.8%, respectively, and these methods correctly estimated the weights of 77.3%, 86.4% and 100% of the foetuses to within 10% of the actual birth weight. The weights of 95.5% of the foetuses were underestimated by the Baker equation. Similar findings were observed among 103 estimations based on both US and MRI within 7 days before delivery. The mean relative error of the MRI-determined estimate of foetal weight using the modified Baker equation was not significantly associated with foetal sex, birth weight, gestational age at MRI examination, the MRI-to-delivery interval or the type of MRI scanner.

CONCLUSION: A modified Baker equation with a high-density coefficient can improve the accuracy of foetal weight estimation based on 3D MRI foetal volume at term, and its accuracy was not significantly affected by foetal characteristics or the type of MRI scanner among births occurring within 7 days after examinations.