Uterine effusion is the accumulation of fluid in the uterine cavity, and uterine effusion is detected by ultrasound. The causes of uterine fluid are as follows: 1. If you are in your menstrual period when you do the ultrasound, because there is blood in the uterine cavity, at this time, you can see the fluid in the uterine cavity or the blood in the uterine cavity under the ultrasound, which is a physiological situation; 2. Normally, it can be discharged out of the body through the vagina. If uterine fluid is detected under ultrasound, there are 2 situations. One is excessive fluid accumulation, i.e., excessive secretion, and the other is foreign body blockage, which cannot be discharged, mostly the 2nd situation. The first condition, excessive discharge, is often present in patients with heavy bleeding i.e. heavy menstrual flow, which can be seen on ultrasound. Then, pelvic inflammatory disease leads to uterine congestion and edema, and the secretion increases and is not discharged smoothly. In addition to this, the phenomenon of obstruction, i.e., there is a foreign body in the uterine cavity that prevents the discharge. During the examination, the patient’s medical history should be asked. If there is a history of uterine operation, such as IUD, removal of IUD, or fluid accumulation after abortion, attention should be paid to whether it is due to surgical injuries resulting in uterine adhesion or cervical tube adhesion, leading to fluid or blood accumulation and poor drainage. Secondly, there are various endometrial diseases. Inflammation of the endocervical lining leads to adhesions, and the menstrual flow is not discharged. Secondly, there are also tumors, tumors in the cervical canal or in the uterine cavity close to the endometrium, such as submucous fibroids and cervical polyps, which can lead to poor drainage of fluid. Older people due to menopause uterine atrophy, if after atrophy and secretion, this can cause poor drainage. The cause of effusion is due to inflammation, so the elderly can sometimes detect the accumulation of pus in the uterine cavity; 3, malignant lesions such as endometrial carcinoma, this time the secretion is very much and poorly discharged, at this time, there is no obvious clinical symptom, which can be detected through the examination, and it should be tracked down; to summarize, the cause of uterine effusion can be physiological, and there will be the problem of uterine blood accumulation in the examination of the menstruation period. Pathologic, pathologic due to pelvic inflammatory disease, menorrhagia, etc., resulting in blood or excessive secretions and not timely discharged, the formation of ultrasound uterine cavity fluid. It can also be pathologic, such as adhesions to the cervical canal, obstruction of the cervical canal by a mass in the uterine cavity, or in the elderly, the uterine opening is too tight due to uterine atrophy, and the secretions in the cavity are not discharged properly. Further investigation should be made, especially to exclude malignant lesions.