Hi, Mirena is a hormonal intrauterine device that can provide long term birth control. The device is a T shaped plastic frame that is inserted into the uterus, where it releases a type of the hormone progestin. To prevent pregnancy, Mirena thickens mucus in the cervix to stop sperm from reaching or fertilizing an egg and thins the lining of the uterus and partially suppresses ovulation. It prevents pregnancy from any type of unprotected sexual intercourses for up to five years after insertion. You can do test for pregnancy 7 days after a missed period. If your pregnancy test becomes positive, then you should consult your doctor promptly. Side effects of Mirena IUD are nausea, vomiting, bleeding or spotting between periods, irregular uterine bleeding, mood changes, abdominal pain or cramps, fatigue, tiredness, acnes, breast tenderness and enlargement, headache, mood swings, depression, vaginal discharge, vaginal bleeding, weakness etc. If these side effects persist for long or bother you, then you can consult your doctor for medical help. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician