Endometrial thickness 12mm physiological causes are not serious, pathological causes are more serious, the answer can not be generalized, for example, secretory period endometrial thickness 12mm is not serious, after the clean menstruation, postmenopausal endometrial 12mm is relatively serious. Women’s endometrial thickness will vary with the menstrual cycle, the endometrial thickness is different in different cycles, and its standard is also different. The endometrial thickness at the end of menstruation is 2-4mm, at this time, the endometrial thickness of 12mm is abnormal, belongs to the endometrial thickening, whether it is serious or not should be examined to determine, for example, ovarian dysfunction caused by the endometrial lining is not considered serious, and can be restored to normal after symptomatic treatment. The endometrial thickness of 12mm caused by endocrine functional tumors is not so serious because of the slow development of the disease in the early stage, which is not easy to metastasize and spread, and the disease is not so serious, while the malignant endocrine tumors in the middle and late stages develop rapidly, and metastasize and spread through infiltration, bloodstream and lymphatic system, and the disease is relatively serious. After menstruation, the endometrium will be gradually thickened under the influence of increased hormone level, and the thickness of endometrium in secretion period can reach 10-15mm before the next menstruation, usually not more than 15mm, and the thickness of endometrium of 12mm is normal at this time. The endometrial thickness of 12mm after complete menopause is not normal, and the endometrial thickness after menopause is not more than 5mm, which is considered as endometrial polyp, which is not so serious. It is endometrial thickening caused by endometrial cancer, which is not so serious in early stage and more serious in middle and late stage. The endometrial thickness of 12mm alone is not enough to determine whether it is normal or serious, you have to go to the hospital for examination and judgment.