Measurement of fetal head descent using the `angle of progression' on transperineal ultrasound imaging is reliable regardless of fetal head station or ultrasound expertise.

The article presents a study that aims to find out measurement reliability when images were obtained by some operators with varying ultrasound experience. It cites that intraclass correlation coefficients (ICCs) having 95 percent confidence interval (CI) were used to measure interobserver reliability and Bland-Altman test was used to assess interobserver agreement. It states that transperineal ultrasound imaging's angle of progression measurement is reliable despite ultrasound experience.