IUS and IUD: Related but Distinct Terms
IUS (Intrauterine System) and IUD (Intrauterine Device) are related terms that are often used interchangeably, but technically IUS refers specifically to hormone-releasing intrauterine devices, while IUD is the broader umbrella term that encompasses both hormonal and non-hormonal devices. 1
Terminology Clarification
IUD as the Umbrella Term
- IUD (Intrauterine Device) is the general term that includes all devices placed in the uterus for contraception, regardless of whether they release hormones 1
- The CDC uses "IUD" to classify both the levonorgestrel-releasing device (LNG-IUD) and the copper-bearing device (Cu-IUD) 1
IUS as a Specific Subtype
- IUS (Intrauterine System) specifically refers to hormone-releasing devices, particularly the levonorgestrel-releasing system 2, 3
- The levonorgestrel-releasing IUS releases 20 μg of levonorgestrel daily from a 52 mg reservoir 2, 4
- IUDs and subdermal implants are classified as progestin-only contraceptives by the CDC 5
The Two Main Types
Hormonal Device (LNG-IUS/LNG-IUD)
- Contains levonorgestrel (a progestin hormone) 1, 2
- Approved for 5 years of contraceptive use, with evidence supporting up to 7 years of effectiveness 2
- Causes dramatic reduction in menstrual bleeding, with 15-20% of users becoming amenorrheic after 1 year 2, 3
- Pearl index of 0.1 per 100 woman-years 3, 4
Non-Hormonal Device (Cu-IUD)
- Contains copper as the active contraceptive agent 1, 6
- Can be used for 10 years before replacement 6, 4
- May increase menstrual blood loss and dysmenorrhea in some women 6, 7
- Cumulative pregnancy rates of approximately 3-5 over 10 years 4
Clinical Implications
Both devices are highly effective contraceptives with failure rates less than 1% per year 5, 2, 3
Common Features
- Neither device protects against sexually transmitted infections or HIV 1, 8
- Both are appropriate for nulliparous women, adolescents, and women in various medical conditions 5, 7
- Both can be inserted immediately postpartum or post-abortion 1, 7
Key Differences in Clinical Use
- The LNG-IUS provides therapeutic benefits for menorrhagia, dysmenorrhea, endometriosis, and adenomyosis 9, 2, 7
- The Cu-IUD can be used as emergency contraception with close to 100% effectiveness 7
- The Cu-IUD is preferred for women who cannot or choose not to use hormones 6
Practical Takeaway
In clinical practice, when someone says "IUD," they could be referring to either type of device, so clarification is important. The term "IUS" is more commonly used in international literature and by manufacturers to specifically denote the hormonal levonorgestrel-releasing system, while U.S. guidelines typically use "LNG-IUD" and "Cu-IUD" to distinguish between the two types 1, 2.