Objective: The aim of our study was to asses the validity of the ultrasound measurements, effect of the operator on the measurement and to find most accurate parameters for the monitoring of the bladder neck. Design: Pilot study. Setting: Obstet. Gynecol Department, General teaching hospital, Ist Medical Faculty, Charles University, Prague. EuroMISE centre of the Charles University and Academy of Sciences, Prague, Czech Republic. Methods: 50 women were included in the study. The coordinate system was defined as follows: the x axis is the axis of the symphysis, with 0 at lower edge of the symphysis. The y axis is perpendicular to x. In this system the rotational angle gama (γ) and distance (p) were measured. The measurements were taken at rest and during maximal Valsalva, repeated independently twice by each observer.Reliability of measurements was statistically tested. Results: The vector of movement (distance between the position of the point at rest and at maximal Valsalva) shows a typical error of 2.2 and 2.4 mm for Operator 1 and 2, respectively. For Operator 1 the shift between two measurements was 2.1 (SD 1.5 mm); for Operator 2 the value was 3.3 (SD=1.7mm), (differences between the operators are statistically significant). Differences at maximal Valsalva were similar. While the variability in measuremets is similar for both operators, this does not mean that final measurements are the same. The vector of the movement is not influenced by the variability of the measured parameters. Conclusions: Differences between the operators are probably due to different placement of the axis of the symphysis, as there are minimal differences in vector of movement. Statistical evaluation indicates that the differences between the operators are statistically significant.

        Key words: transperineal ultrasound, stress urinary incontinence, bladder neck