Study subjects
This cross-sectional observational study was performed at Sun Yat-sen
Memorial Hospital of Sun Yat-sen University. From January 2018 to March
2020, 172 consecutive premenopausal women from the gynecology clinic
center who were referred for pelvic ultrasonography were included. The
inclusion criteria were as follows: 1) childbearing age; 2) with regular
menstrual cycle; 3) pelvic and ultrasonic examination revealed normal
sized uterine body; 4) had a normal uterine cavity on two- and
three-dimensional transvaginal ultrasonography; 5) no history of uterine
cavity surgery before the ultrasonography; 6) the subsequent
hysteroscopy confirmed normal uterine cavity (without fibroids,
endometrial polyps, uterine synechiae and intrauterine device). The
exclusion criteria included the following items: 1) thickened
endometrium (≥15mm); 2) simple or atypical endometrial hyperplasia, or
endometrial malignancies; 3) having used contraceptives or any other
kind of hormones in the 3 months before participating in the study; 4)
had a history of pregnancy in the 6 months preceding the ultrasound
scan.