Comparison of magnetic resonance imaging to ultrasound in the estimation of birth weight at term

Objective This study was undertaken to compare magnetic resonance (MR) and ultrasound (US) fetal weight estimates obtained immediately before delivery with birth weight. Study design Eighty women scheduled for a cesarean delivery underwent a fast acquisition MR and US for fetal weight estimation within 3 hours of delivery. Prospective MR calculation was based on the equation 0.12 + 1.031 g/mL×fetal volume (mL) = MR weight (g). US fetal weight estimation was calculated by the formula by Hadlock et al. Estimations were compared with birth weight. Results Correlation (95% CI) between birth weight and MR weight is 0.95 with a mean absolute error of 129 g (105–155) compared with the correlation between birth weight and US of 0.85 with a mean absolute error of 225 g (186–264). The correlation for birth weight and MR imaging is significantly greater than that of birth weight and US, P<.001. Conclusion Birth weight estimation is more accurate by MR imaging than by US in term infants.