It is not normal for menstruation to be delayed in the fourth month after the implantation of the IUD. Considering that it may be caused by abnormalities of the IUD or gynecological inflammation, it is recommended to go to the hospital in time for relevant examinations to clarify the cause of the disease and then take treatment. 1. Abnormal birth control ring: Delayed menstruation in the fourth month after the implantation of the ring is abnormal. You can go to the hospital to check whether the position of the IUD has shifted downward and other symptoms. The IUD may cause mechanical pressure on the endometrium, resulting in poor blood circulation to the endometrium, causing endometrial necrosis, ischemia and other conditions. 2. Gynecological inflammation: If the patient has gynecological inflammation, it may also lead to the phenomenon of delayed menstruation. Patients should pay attention to keep warm, rest more, avoid exertion, and keep a balanced diet.