The intrauterine device (IUD) is a form of birth control; it is an object placed in the uterus to prevent pregnancy.
Among modern IUDs, the two types available are copper-containing devices, and a hormone-containing device that releases a progestogen. Currently, there are over 10 different kinds of copper IUD available in different parts of the world, and there is one hormonal device, called Mirena.
Copper IUDs work by impairing the mobility of sperm and preventing them from joining with an egg. Additionally, the foreign body inside the uterus irritates the lining and wall making it hard for an embryo to implant.
Most non-hormonal IUDs have a plastic T-shaped frame that is wound around with pure electrolytic copper wire and/or has copper collars (sleeves). The Paragard T 380a is 32 mm (1.26″) in the horizontal direction (top of the T), and 36 mm (1.42″) in the vertical direction (leg of the T). In some IUDs, such as the Nova T 380, the pure copper wire has a silver core which has been shown to prevent breaking of the wire. The arms of the frame hold the IUD in place near the top of the uterus.
Hormonal uterine devices (sometimes called IntraUterine Systems) do not increase bleeding as copper-containing IUDs do. Rather, they reduce menstrual bleeding or prevent menstruation altogether, and can be used as a treatment for menorrhagia (heavy periods). Although use of IntraUterine Systems results in much lower systemic progestogen levels than other very-low-dose progestogen-only hormonal contraceptives, they might possibly have some of the same side effects.