Intraobserver and interobserver reproducibility of ultrasound measurements of endometrial thickness in postmenopausal women

Objectives To determine intraobserver and interobserver reproducibility of ultrasound measurements of endometrial thickness in postmenopausal women. Design Forty-eight postmenopausal women underwent transvaginal ultrasound examination by two examiners. Each observer took three replicate measurements of the endometrium in each woman. Intraobserver repeatability was expressed as the difference between the highest and lowest measurement values obtained by one observer, the repeatability coefficient, and the intraclass correlation coefficient. Interobserver reproducibility was expressed as the difference between the mean of the three measurements of each observer, limits of agreement, and interclass correlation coefficient. The repeatability coefficient and the limits of agreement define the range within which 95% of the differences between two measurements are likely to fall. Data were analyzed for all women, as well as separately for women with endometrium less than or equal to 6 mm and > 6 mm. The agreement between observers in classifying women as having endometrium less than or equal to 4.4 mm or greater than or equal to 4.5 mm was determined by calculating Cohen's kappa. Results In women with endometrium: 6 mm the intraclass correlation coefficient was 0.95 for Observer 1 and 0.88 for Observer 2, the median difference between the highest and lowest values being 0.4 mm (range, 0-1.4) for Observer 1 and 0.7 mm (range, 0.1-2.2) for Observer 2, and the repeatability coefficient was 0.8 mm and 1.4 mm, respectively. The corresponding figures for women with endometrium > 6 mm were 0.99 and 0.99, 0.7 mm (0-2.9) and 1.0 mm (0.2-3.4), and 1.7 mm and 1.9 mm. In women with endometrium less than or equal to mm the interclass correlation coefficient was 0.77, and the mean interobserver difference was 0.2 mm +/- 1.8 mm (2 standard deviations), when calculations were based on the mean of three measurements per observer (1.9 mm when calculations were based on only one measurement per observer). The corresponding figures for women with endometrium > 6 mm were 0.98, 0.2 mm +/- 3.1 mm (3.2 mm). The agreement between observers in classifying women as having an endometrium less than or equal to 4.4 mm or greater than or equal to 4.5 mm was very good (kappa 0.81). Conclusions The reproducibility of endometrial measurements seems to be clinically acceptable and to allow reliable discrimination between postmenopausal women with endometrium less than or equal to 4.4 mm and greater than or equal to 4.5 mm. In clinical practice, it is enough to take one endometrial measurement when performing transvaginal ultrasound examination.