IUD contraceptive insertion tool. This intrauterine device (IUD), made by Mirena, is a T-shaped piece of plastic that releases low doses of progesterone. It is inserted in the uterus (womb) to prevent pregnancy. The presence of the device and the addition of the female sex hormone progesterone, both help prevent a fertilised egg implanting in the uterine wall. The progesterone is released for up to 5 years, after which the device is removed.