Changes in ultrasound uterine morphology and endometrial thickness during ovarian aging and possible associated factors: findings from a prospective study.

OBJECTIVE: The aim of the study was to provide reference values for sonographic measurements of uterine morphology, quantify changes in uterine morphology across the menopausal transition, and identify possible factors associated with sonographic findings in uterine morphology. METHODS: This is a longitudinal cohort study conducted in middle-aged Chinese women. Using transvaginal ultrasound, we measured morphologic parameters of the uterus (volume and endometrial thickness) under standardized conditions every year for over a decade. RESULTS: Uterine volume begins to decrease before the final menstrual period and declines rapidly thereafter. Compared with a baseline measurement taken in the year of the final menstrual period, uterine volume decreased by 20% and 35% at the first year and second year of postmenopause, respectively. The rate of decrease was slower in the third year. Compared with endometrial thickness in the year of the final menstrual period, the figures for 2 and 3 years before the final menstrual period were 5% and 10% higher, while they decreased by 9% and 18% at the first and second year after the final menstrual period. Similarly, the endometrial thickness became relatively stable 3 years after the final menstrual cycle. These observations were fairly consistent across all women without uterine fibroids. Endometrial thickness was significantly positively associated with body mass index (P = 0.049) after adjusting for time and menopausal stage. CONCLUSIONS: The figures for uterine volume and endometrial thickness decrease around menopause using ultrasound measurments with large reductions in the first and second year after the final menstrual period. A higher body mass index is associated with increased endometrial thickness.