The luteal phase refers to the days before the onset of menstruation, which may cause bleeding at this time. The specific cause of bleeding may be due to the fact that after the mature follicle ruptures and ovulates, the estrogen level drops sharply and significantly, which cannot sustain the growth of the endometrium, causing the superficial layer of the endometrium to break down and shed locally, resulting in breakthrough bleeding in small amounts, which is discharged with the formation of the corpus luteum of the ovary, resulting in small amounts of bleeding. However, if a person has inflammatory lesions in the vagina or cervix, it may cause a blood-like dark brown fluid to be discharged, creating the illusion of bleeding, which is metabolic waste produced by inflammatory pathogenic bacteria. It is also important to see if there is any possibility of pregnancy, as the luteal phase may have occurred during the last month, causing a small amount of vaginal bleeding. If the bleeding is heavy, it is important to pay attention to the possibility of pre-eclampsia, and it is recommended to go to the hospital for examination to determine this.