A little vaginal bleeding before the time of menstruation is often due to luteal insufficiency. After ovulation by the ovaries, the corpus luteum forms and secretes progesterone to thicken the endometrium. When the corpus luteum does not function sufficiently, the endometrium will shed and bleeding will occur. Therefore, this bleeding phenomenon can be improved with progesterone supplementation during the second half of menstruation. It is also clinically recommended to exclude the possibility of endometrial inflammation, or submucosal fibroids or endometriosis. It is recommended to have an ultrasound examination after menstruation to find out if there are any organic lesions. In addition, a blood test for sex hormone six should be done on the second day of menstruation to understand the endocrine situation and whether the bleeding is caused by luteal insufficiency.