ABSTRACT: Objective To evaluate the intra-observer and inter-observer replicability of the measurements obtained from three-dimensional (3D) transperineal ultrasound in the second labor. Methods The ultrasonic parameters were obtained from 48 primiparous women (single birth, head-presentation) in the second stage of labor every 15 minutes, from Mar. 2016 to Sep. 2016, which were scored and separately evaluated by two different operators using the Sono VCAD labor software. The following ultrasonic parameters were measured: head progression angle, head progression distance, head direction, and midline angle. The intra-group correlation coefficient and Bland-Altman analysis method were used to evaluate the intra-observer and inter-observer replicability of the ultrasonic parameters. Results (1) Of the four ultrasonic parameters, the inter-observer deviation was higher than the intra-observer one. (2) The replicability of the other three ultrasonic parameters were better than that of the midline angle. Among them, labor progress and head progression distance had better replicability. Conclusion During monitoring the progress of the second stage of labor with 3D transperineal ultrasound, labor progress and head progression distance had good replicability, indicating that these two ultrasonic parameters were the reliable indicators to assess fetal head progression.