The normal endometrium is about 1 cm thick when it is discharged and shed during menstruation. After menstruation is the time when the endometrium is at its thinnest and before menstruation is when the endometrium is at its thickest. The shed endometrium is not all endometrium shed. The endometrium has two layers, the basal layer and the functional layer, and the hormonal cycle changes in a woman’s body will affect the thickness of the functional layer. The endometrium shed during menstruation is the hormonally influenced, proliferating, thickened functional layer that appears during menstruation. After menstruation clears, the basal layer will again repair the endometrium to form a new functional layer according to the hormonal changes. If the level of hormonal cycle changes in the body is not enough, the function becomes accretion and the thickness becomes smaller. In the case of women of childbearing age, the level of hormonal changes is low and the thickness of the endometrium before menstruation is still relatively thin, below 0.7cm it is difficult to get pregnant.