The IUD is similar to the IUS (intrauterine system) but works in a different way. Instead of releasing the hormone progestogen like the IUS, the IUD releases copper. Copper changes the make-up of the fluids in the womb and fallopian tubes, stopping sperm surviving there. IUDs may also stop fertilised eggs from implanting in the womb. An IUD can stay in the womb for five to 10 years depending on the type.