An endometrial lining of 0.9mm three days after the menstrual period needs to be assessed in relation to the patient’s own menstrual period and cycle time, which is more often than not abnormal and thicker compared to normal. However, if the menstrual period itself is at the upper limit of normal and the menstrual cycle is at the lower limit of normal, this thickness may be normal. 1 Since normal menstruation is formed by the stripping of the endometrium, and although the endometrium grows gradually after menstruation is cleared by estrogen, an endometrial thickness of 0.9 mm is on the thicker side for a patient who has been cleared for three days, and is considered to be related to endocrine disorders, endometrial polyps, and so on. For patients with endocrine disorders, the patient will have irregular ovulation, resulting in insufficient levels of progesterone in the body, failing to make the endometrium undergo an endocrine phase response, and therefore can not be completely peeled off; for patients with endometrial polyps, due to polyps occupying the uterine cavity, the endometrium will be thicker, and at the same time, ultrasound can be found in the hypoechoic-like changes. 2. For some patients, such as their own menstrual period in the upper limit of normal, while the menstrual cycle in the lower limit of normal, although the menstrual period is clean for three days, may be in the ovulation period, it may be normal. For patients with endometrium of 0.9mm for three days after the menstrual period, it is recommended to go to the hospital and improve the ultrasound and other related examinations, which need to be evaluated by the doctor to clarify whether it is normal or not.