Fetal shoulder measurements with MRI

We studied the ability of MRI to predict fetal shoulder width (FSW). In 30 patients referred for MR pelvimetry, measurement of FSW was performed and compared with caliper measurements at term. We report here the feasibility of a method using axial and coronal MR images oriented to the fetal body axes. Shoulder width by MRI (mean = 12.76 +/- 1.42 cm) correlated significantly with postnatal orthopedic caliper measurements (mean = 12.99 +/- 1.37 cm; r = 0.955, SEE = 4.29 mm, p = 0.00001) and with birth weight (r = 0.63, p = 0.0005). Mean paired differences showed a statistically significant 2.3 +/- 4.2 mm underestimation of FSW by MRI (p = 0.01). This reasonably quick nonionizing technique seems to have the potential for evaluating shoulder dystocia and deserves further evaluation.