Intrauterine Devices (IUDs)

An intrauterine device is a small device placed inside the uterine cavity to provide long-acting reversible contraception. The two principal types are the copper device, which prevents fertilization through a copper-induced inflammatory and spermicidal effect, and the levonorgestrel-releasing intrauterine system, which adds local progestogen effects on cervical mucus and the endometrium.

Definition

An intrauterine device is a contraceptive device inserted into the uterine cavity that prevents pregnancy by local effects on sperm, fertilization, and the endometrium, available in copper-bearing and levonorgestrel-releasing forms.

Scope

This entry covers the mechanisms of copper and hormonal intrauterine devices, their high effectiveness as long-acting reversible methods, and their place within the medical eligibility framework. It is a reference overview of how these devices work and how their effectiveness is established, not insertion or prescribing guidance.

Core questions

• How do copper and levonorgestrel intrauterine devices differ in mechanism?
• Why do intrauterine devices achieve among the lowest typical-use failure rates?
• What distinguishes the device's contraceptive action as primarily pre-fertilization?

Key concepts

• Copper intrauterine device
• Levonorgestrel intrauterine system
• Long-acting reversible contraception
• Spermicidal copper effect
• Cervical mucus thickening
• Pre-fertilization mechanism
• Continuation and reversibility

Mechanisms

Ortiz and Croxatto (2007) describe how copper devices release copper ions that produce a sterile inflammatory reaction in the uterine cavity and are toxic to sperm and ova, impairing sperm motility and viability so that fertilization is prevented in the great majority of cycles. The levonorgestrel-releasing intrauterine system adds a local progestogen effect that thickens cervical mucus, suppresses the endometrium, and impairs sperm function. Both types act predominantly before fertilization. Because effectiveness does not depend on user adherence, intrauterine devices are among the most effective reversible methods, as shown in the cohort study of Winner and colleagues (2012).

Clinical relevance

Intrauterine devices are recommended within long-acting reversible contraception strategies because of their high effectiveness and convenience, and eligibility is assessed against medical criteria such as those of the World Health Organization. The copper device also has a recognised role as a highly effective form of emergency contraception. This entry describes mechanisms and effectiveness evidence at a reference level and is not a basis for individual clinical decisions.

Epidemiology

Trussell (2011) reports typical-use failure rates for both copper and hormonal intrauterine devices of well under one percent per year, comparable to sterilization and far lower than short-acting methods. Winner and colleagues (2012) found that participants using intrauterine devices and implants had markedly lower contraceptive failure than those using pills, patches, or rings.

History

Intrauterine contraception evolved from early inert rings in the first half of the twentieth century to plastic devices, and then to copper-bearing devices introduced in the 1960s and 1970s that substantially improved effectiveness. The levonorgestrel-releasing intrauterine system later combined the long-acting reversible advantages of the device with local hormonal effects, broadening the method's clinical applications.

Seminal works

• ortiz-croxatto-2007
• winner-2012
• trussell-2011

Frequently asked questions

How does a copper intrauterine device prevent pregnancy?

Copper ions released by the device create an inflammatory environment in the uterus and are toxic to sperm, impairing sperm movement and viability so that fertilization is prevented in most cycles; its action is primarily before fertilization.

Why are intrauterine devices so effective in everyday use?

Once placed, an intrauterine device works for years without any action by the user, so there is no opportunity for the missed doses or inconsistent use that lower the effectiveness of pills and condoms.