MRI-Derived Fetal Weight Estimation in the Midpregnancy Fetus: A Method Comparison Study

Abstract

<b><i>Objectives:</i></b> The aim of this study was to compare the standard ultrasound (US) estimated fetal weight (EFW) and MRI volume-derived methods for the midtrimester fetus. <b><i>Methods:</i></b> Twenty-five paired US and MRI scans had the EFW calculated (gestational age [GA] range = 20–26 weeks). The intra- and interobserver variability of each method was assessed (2 operators/modality). A small sub-analysis was performed on 5 fetuses who were delivered preterm (mean GA 29 <sup>+3</sup> weeks) and compared to the actual birthweight. <b><i>Results:</i></b> Two MRI volumetry EFW formulae under-measured compared to US by −10.9% and −14.5% in the midpregnancy fetus (<i>p</i> < 0.001) but had excellent intra- and interobserver agreement (intraclass correlation coefficient = 0.998 and 0.993). In the preterm fetus, the mean relative difference (MRD) between the MRI volume-derived EFW (MRI-EFW) and actual expected birthweight (at the scan GA) was −13.7% (−159.0 g, 95% CI: −341.7 to 23.7 g) and −17.1% (−204.6 g, 95% CI: −380.4 to −28.8 g), for the 2 MRI formulae. The MRD was smaller for US at 5.3% (69.8 g, 95% CI: −34.3 to 173.9). <b><i>Conclusions:</i></b> MRI-EFW results should be interpreted with caution in midpregnancy. Despite excellent observer agreement with MRI volumetry, refinement of the EFW formula is needed in the second trimester, for the small and for the GA and preterm fetus to compensate for lower fetal densities.

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“…The longest mean VLM in the MP was reported for the single-rooted MFP (8.39±2.80 mm and 7.50±3.51 mm), followed by the BR of the double-rooted MFP, while a shorter distance was seen in the PR. The shortest distance in the MP was between the PR of the MSP and the MSF (right, 2.11±5.00 mm; left, 1.67±2.06 mm) (Table 6); these measurements are in line with what was reported by many preceding studies [6,14,19,20,26].…”