Bleeding on the sixth day of IUD may be related to endometrial damage, improper choice of IUD, external stimulation and other reasons. 1. Damage to the uterine lining: as a foreign body in the uterine cavity, the IUD will cause local damage to the uterine lining, which will lead to bleeding on the sixth day of the IUD, and if the bleeding gradually decreases until it stops, it is possible to continue to wear the IUD. 2. Improper choice of birth control ring: If the ring size of the birth control ring is not chosen properly, it may hurt the myometrium of the uterus, which may lead to bleeding on the sixth day of the IUD. 3. External stimulation: If you have intercourse within a short period of time after the IUD is inserted, and your body is still in the recovery stage, this external stimulation may cause the ring to rub against the uterine lining, which may cause the blood to start flowing on the sixth day of the IUD. It is recommended that the patient go to the hospital in time for consultation and standardized treatment after clarifying the cause of the disease, so as to avoid delaying the condition.