There are several reasons for dark brown vaginal discharge: 1. If there is dark brown vaginal discharge in the middle of menstruation, it may be ovulatory bleeding because there is a temporary decrease in estrogen secretion after the follicles develop and mature during ovulation, causing a small amount of endometrial shedding and a small amount of uterine bleeding, which will turn dark brown because of the small amount of bleeding and a longer stay in the uterine cavity. 2. 3. Some women may have dark brown vaginal discharge two days after their menstruation starts or two days after their menstruation ends, which is a normal physiological phenomenon due to the small amount of uterine bleeding and the long residence time in the uterine cavity. or uterine cancer.