When black discharge occurs a few days before menstruation, there is a possibility that there is a lack of luteal function. When there is a lack of luteal function, there will be brown discharge occurring in the week or 5-7 days before menstruation. If it occurs once alone, you can observe it for a while. If it occurs frequently, you should take a blood test for endocrine hormones on an empty stomach on the 2nd-5th day of menstruation to see if there is any abnormality. When there is environment, stress, endocrine hormone abnormality, it may happen. It may also be present if there is overwork. However, if you have had unprotected intercourse during the month, you will not have your period at this time, but brown discharge may be present due to preterm miscarriage. It is best to go to the drugstore and buy a pregnancy test, which you can use about 12 days after intercourse to rule out the possibility of conception.