How thick is the lining of the uterus? What is the pattern of menstrual changes? I believe many women have such questions, so follow our footsteps to learn more about it! How thick is the endometrium? The thickness of the endometrium varies from 5 to 10 mm, but the thickness of the endometrium varies at different times: about 9-10 mm in the proliferative phase, 5-6 mm in the secretory phase, and 8-10 mm in the menstrual phase, which varies with the cyclical changes of the ovaries. The endometrium is in the proliferative phase from the 5th day of the menstrual cycle, and the endometrium continues to thicken until the 14th day of menstruation, when it can reach 3-4 mm; in the second half of the menstrual cycle, the endometrium is in the secretory phase, but it continues to thicken until the endometrium is 10 mm thick before the menstrual cycle. Under normal circumstances, the endometrial thickness of a woman is 8 – 12 mm, and the minimum should not be less than 6 mm. Generally speaking, the thickness of the endometrium is around 10 mm after the first pregnancy. Experts say that the thickness of the endometrium that is conducive to conception is about 8 mm. The best time for conception is during the luteal phase. Why does the lining thicken? Endogenous estrogen (1) Non-ovulation: In adolescent girls, perimenopausal women, hypothalamic-pituitary-ovarian axis disorders, polycystic ovary syndrome, etc., there can be non-ovulation, so that the endometrium is continuously affected by estrogen for a longer period of time, without progesterone counteracting it, lacking the transformation of the cyclic secretory phase, and in a state of proliferation for a long time. In addition to focal atypical hyperplasia, more than 80% of the endometrium has no secretory phase; 70% of the basal body temperature measurements are monophasic. Therefore, most patients have no ovulation. (2) Obesity: In obese women, androstenedione secreted by the adrenal glands is converted into estrone by the action of aromatase in adipose tissue; the more adipose tissue there is, the stronger the conversion ability, and the higher the plasma level of estrone, thus causing persistent estrogenic effects. (3) Functional endocrine tumors: Functional endocrine tumors are rare tumors, but 7.5% of them are endocrine functional tumors in research statistics. The pituitary gland has abnormal gonadotropic function, and ovarian granulosa cell tumors are also persistent estrogen-secreting tumors.