Angle of progression measurements of fetal head at term: a systematic comparison between open magnetic resonance imaging and transperineal ultrasound

Objective During labor, transperineal sonography is increasingly used to evaluate fetal head descent. The aim of this study was to compare the angle of progression assessed by open magnetic resonance imaging (MRI) vs transperineal ultrasound. Study Design A total of 31 pregnant women at term (>37 weeks), who were not in labor, underwent MRI in an open 1.0-T system. A midsagittal plane of the maternal pelvis was stored. Immediately after, without changing the supine position, a transperineal ultrasound was performed. The angle of progression was measured offline by transperineal ultrasound and MRI. Results The angles of progression measured by transperineal ultrasound (mean, 79.05 degrees; SD 11.44) and MRI (mean, 80.48 degrees; SD 11.06) correlated significantly ( P < .001). The intraclass correlation coefficient between the 2 methods was 0.89 (95% confidence interval, 0.78–0.94). Conclusion The angle of progression measurements obtained by transperineal ultrasound and open MRI showed very good agreement.