The thickness of the endometrium varies depending on the stage of the menstrual cycle that the body is in; it can vary from 2 millimeters during menstruation to 16 millimeters in the secretory phase. The normal thickness also depends on medical history, explains Dr. Alexandra Stanislavsky from Radiopaedia.org.
The thickness of the endometrium is determined by a transvaginal ultrasound. In premenopausal patients, there is significant variance in readings, but in postmenopausal patients, the use of drugs such as tamoxifen or a history of vaginal bleeding needs to be considered when interpreting the results, reports Radiopaedia.org. Ultrasound is used for visual inspection of the size and shape of the endometrium in order to help make a diagnosis.