Whether the endometrial thickness of 12mm is normal or not, it is important to clarify the specific time period in which it occurs in order to determine if it is normal. It is normal for the endometrium to become thicker, possibly up to 12mm, just before the upcoming menstruation. If the thickness of the endometrium is 12mm 3-7 days after the menstruation clears, it is not normal because the endometrium sheds with the cleansing of the menstruation and it will be thinner at this time, maybe around 4-5mm. The thickening of the endometrium may also be caused by menstrual irregularities or gynecological inflammation endometrial polyps, the specific also go to the hospital to do relevant tests to clarify the diagnosis, such as abdominal ultrasound, if necessary, you can also consider using drugs for treatment, such as taking progesterone or uterine blood granules. It is also necessary to pay special attention to endometrial cancer, which may be accompanied by atypical hyperplasia of the endometrium. When women are approaching menopause, they may also have endometrial thickening, but it is not too obvious. In this case, it is necessary to observe more, go to the hospital every 2-3 months to review ultrasound, and eat more nutritious food.