A small amount of menstruation may be caused by ovulation bleeding, or considered to be caused by polycystic ovary syndrome, uterine cavity adhesion and other diseases. 1. Ovulation bleeding: Due to the change of estrogen level in women’s body, it may lead to partial shedding of endometrium before menstruation, which is manifested as a small amount of bleeding. Some patients may mistake it for menstruation with a little blood. 2. Polycystic Ovary Syndrome (PCOS): The cause of PCOS is not yet clear, and it may be due to genetic and environmental factors. Patients may have scanty menstruation, irregular menstruation, varying amount of menstruation, hairiness, acne and other symptoms, which are manifested as a little bit of menstruation. 3. Uterine adhesion: The cause of uterine adhesion may be related to endometrial trauma, infection, low estrogen level, heredity and other factors. Patients may experience symptoms such as decreased menstrual flow and cyclical abdominal pain, which manifests itself as a little bit of menstruation. There are many reasons for a little bit of menstruation, patients need to go to the hospital in time, so as to clarify the cause of the disease.