Measurement precision and normal range of endometrial thickness in a postmenopausal population by transvaginal ultrasound

OBJECTIVES: The aim of this study was to examine the endometrial thickness (ET) in an asymptomatic postmenopausal population, and to assess the long-term variability.

DESIGN: A total of 1182 asymptomatic generally healthy postmenopausal women were enrolled into this cross-sectional evaluation of the ET. Measurements were performed by transvaginal ultrasound. A subset of the women (n = 178) was examined twice 3 months to 2 years apart to assess the long-term variability.

RESULTS: Cross-sectionally, ET varied with length of menopause. During the first 5 years after menopause (YSM) the mean ET was 2.3 mm but it decreased by 0.03 mm/year (P < 0.01). From 5 to 13 YSM the ET remained stable at a mean of 1.8 mm with no significant changes (P = 0.13). Thereafter there was a minimal increase of 0.01 mm/year (P < 0.05). In order to minimize the influence of natural changes on ET, only women who had reached the menopause more than 5 years earlier were entered into the subsequent long-term study. The mean ET was 2.0 mm +/- 1.0 mm with no significant differences within or between the observers' measurements. The precision errors were less than 1 mm.

CONCLUSIONS: The normal range of the thickness of the postmenopausal endometrium in asymptomatic women varies with YSM. There is a high long-term agreement within and between observers in measuring the ET.