The area where the uterus meets the rectum is the lowest point of the pelvic cavity and often presents as a sunken depression called the utero-rectal sink. Since this depression is parallel to the posterior vaginal fornix, the doctor can identify the situation by posterior fornix puncture when there is a large accumulation of fluid or blood. In general, if there is no fluid accumulation in the recto-uterine sulcus, or if a small amount of fluid accumulates during ovulation or early pregnancy, there are usually no uncomfortable symptoms and the fluid will be gradually absorbed. However, if there is a large amount of fluid in the abdomen, accompanied by abdominal pain, swelling and other discomfort, it is considered to be caused by ectopic pregnancy rupture, corpus luteum rupture, pelvic inflammatory disease, pelvic tumor, etc. Patients need to perform a puncture examination to clarify the nature of the fluid and then carry out targeted treatment according to the cause. In addition, the rectal recess is usually the site of endometriosis nodules. If menstrual blood is planted in the rectal recess and regularly shed and bleed, a painful nodule will be formed, called a pelvic endometriosis nodule. If diagnosed, the patient is treated with appropriate specific medication or surgery. In daily life, patients need to ensure cleanliness and hygiene of their reproductive organs to avoid infection, which may lead to worsening of symptoms.