Detailed medical illustration of a copper IUD inserted in the uterus, showing its T-shaped copper wire design. This contraceptive device prevents pregnancy by affecting sperm mobility and egg ferti...
An IUD works primarily by preventing sperm from reaching and fertilizing an egg. Hormonal IUDs thicken cervical mucus and may thin the uterine lining, while copper IUDs create an environment that is toxic to sperm. Both types are over 99% effective when properly placed.
Hormonal IUDs release a small, steady amount of progestin. This hormone thins the uterine lining, making it less suitable for implantation. In many users, it also leads to lighter periods — or no periods at all.
Fertilization typically occurs in the fallopian tubes, not inside the uterus. An IUD works before this stage by interfering with sperm movement and survival, making fertilization highly unlikely.
The thin strings extend slightly into the vaginal canal so placement can be checked. A healthcare provider can confirm positioning during an exam, and some patients are taught how to gently feel for the strings at home.
Although rare, pregnancy can happen if an IUD shifts out of place, is expelled, or was not positioned correctly. If pregnancy does occur with an IUD in place, there is a higher chance it could be ectopic, meaning it develops outside the uterus. Prompt medical evaluation is important if symptoms such as severe abdominal pain or unusual bleeding occur.