Brown discharge 13 days after coitus may be caused by menstrual flow, early pregnancy, miscarriage, ectopic pregnancy, and reproductive endocrine diseases. Brown discharge after 13 days of coitus, if close to the time of menstruation, may be caused by a small amount of menstrual blood after discharge. You should pay attention to rest and avoid catching cold. If you are preparing for pregnancy and have brown discharge after 13 days of coitus, you need to rule out the occurrence of preeclampsia, ectopic pregnancy, etc., which can be clarified by checking human chorionic gonadotropin (HCG) and ultrasound examination. Pre-eclampsia can be treated with fertility preservation according to the patient’s specific situation, and bleeding caused by inevitable miscarriage or ectopic pregnancy requires timely surgical treatment. Brown discharge on the 13th day of coitus, if pregnancy has been ruled out, it may be caused by reproductive endocrine diseases, which can be clarified by female hormone six, thyroid function, ultrasound and so on. The results can be used to treat the cause of the problem. The brown discharge from 13 days of intercourse is recommended to consult a doctor to clarify the cause of the disease, and the use of medication should follow the doctor’s instructions.