Patients often come to the gynecology clinic with a diagnosis of “pelvic fluid” on ultrasound and request treatment. Is pelvic effusion a disease? Does it need to be treated? As we know, the peritoneal cavity contains intestinal tubes, omentum, uterus, fallopian tubes, ovaries, liver and other organs, which are intraperitoneal organs. The peritoneum covers the abdominal organs and the surface of the pelvis and abdominal cavity, and the peritoneum can leak a small amount of fluid, called peritoneal leakage fluid. Leaky fluid is mostly pale yellow, thin and transparent, which can prevent the organs in the peritoneal cavity from adhering to each other to play a lubricating role in intestinal peristalsis. Under normal conditions, the peritoneal leakage fluid is usually less than 200 ml. The pelvic cavity is part of the peritoneal cavity and is in a low position when standing and the rectal recess of the uterus is in the lowest position of the peritoneal cavity when lying down. Therefore, a dark area of fluid is visible in the rectal recess of the uterus on ultrasound, which is also known as pelvic fluid. At the time of ovulation, the amount of fluid may increase due to the discharge of follicular fluid and the oozing of blood from the ovulation incision, and sometimes even ovulation can be seen on ultrasound again, when the amount of pelvic fluid may increase. This peritoneal leakage as well as follicular fluid from ovulation can lead to pelvic effusion, which is a normal physiological phenomenon and does not require treatment. The pelvic fluid, which is often seen in gynecological clinics as an ultrasound indication, is actually a normal physiological phenomenon and does not need to be treated. However, there are five cases worth noting: 1, when there is pelvic inflammatory disease, the peritoneum is stimulated by inflammatory substances, can produce a large amount of exudate, ultrasound examination also has “pelvic fluid”, but at this time is often accompanied by leucorrhea diagnostic yellow, fever and other symptoms of infection, blood laboratory tests such as white blood cells can have abnormal changes. 2.When the amount of free fluid in the abdominal cavity exceeds 200ml due to cirrhosis complicated by increased portal vein pressure, dilated visceral arteries, reduced plasma colloid osmotic pressure and other factors, it is called “ascites”. 3.When suffering from abdominal tumor, the peritoneum is stimulated by inflammatory substances, which can produce a large amount of exudate, and ultrasound examination also has “pelvic fluid”, which often has the clinical manifestations of the primary tumor. 4.In ectopic pregnancy, the local tissue of the lesion will rupture and bleed, and there will be “pelvic fluid” on ultrasonography. 5. Occasionally, there may be bleeding from the ruptured follicle during normal ovulation, or the rupture and bleeding of the corpus luteum after ovulation in the late menstrual cycle, which may cause vague abdominal pain and other symptoms, and at this time there is “pelvic fluid” on ultrasonography. However, if the rupture is bleeding heavily, it will cause symptoms similar to ectopic pregnancy, and at this time, there may be more pelvic fluid on ultrasound, which is a pathological condition and should be seen by a doctor. The above five pathological conditions require prompt consultation with a doctor and, if necessary, emergency treatment.