The uterus is not solid, it has a cavity, so there is an anterior wall and a posterior wall, the endometrium of the anterior wall is one layer and the endometrium of the posterior wall is another layer, these two layers together are called the bilayer of the endometrium. In general, the thickness of the endometrium can be measured clinically either as a single layer or as a double layer. The bilayer measurement reflects the thickness of the entire endometrium and can determine whether the thickness of the endometrium corresponds to the time of menstruation at different times of the patient’s life. If the patient has just had her period, the thickness is usually around 0.3 cm; by the time of ovulation, it should be at least 0.7-0.8 cm; and 1.0 cm before the onset of menstruation, which is a normal endometrial change if this is the case. If there is an abnormal condition, it suggests that you may have certain diseases and need further examination and treatment.