Optimization of fetal weight estimates using MRI: Comparison of acquisitions

OBJECTIVE. The purpose of this study was to determine whether differences are seen in calculation of fetal weight using 5-mm sagittal, 3-mm coronal, and 8-mm axial MRI acquisitions compared with term birth weight and contemporaneous sonography. MATERIALS AND METHODS. Fetal volume measurements were obtained from MRI acquisitions as follows: 5-mm sagittal (2 acquisitions), 3-mm coronal (2 acquisitions), and 8-mm axial (1 acquisition). A 90-sec single-shot fast spin-echo sequence was used. MRI and sonographic studies for fetal weight estimates were performed within 3 hr of term delivery. MRI calculation was based on the equation 0.12 + 1.031 × fetal volume (fetal area x slice thickness) (mL) = MRI fetal weight (kg). The sonographic fetal weight estimate was calculated using the Hadlock formula. MRI and sonographic calculations were compared with birth weight. Concordance coefficient analysis was performed. RESULTS. Thirty-five retrospective fetal calculations were performed. Concordance coefficients, gram weight means and standard deviations (mean ± SD) between birth weight and MRI acquisitions were as follows: 8-mm axial, 0.91 (3,554 ± 431 g); 3-mm coronal, 0.84 (3,752 ± 578 g); and 5-mm sagittal, 0.83 (3,685 ± 567 g), compared with 0.78 (3,518 ± 332 g) for sonography. The MRI axial concordance coefficient was significantly different from that of the sonographic estimates (p = 0.05). MRI axial concordance coefficient was not statistically different from that of the MRI coronal concordance coefficient (p = 0.22) or the MRI sagittal concordance coefficient (p = 0.19). CONCLUSION. Calculated weights from a 90-sec single-shot fast spin-echo sequence MR acquisition with 8-mm-thick slices in the axial plane at term are better than sonographic estimates.