Intrauterine Device (IUD) and Intrauterine System (IUS) Differences

Long-acting reversible contraception is used by many women who do not wish to have children for several years. Of the many methods available, two of the most widely used are the intrauterine device (IUD) and the intrauterine system (IUS).


The intrauterine system

The IUS is a slender T-shaped device with flexible arms that contains progestogen. This hormone is the synthetic equivalent of the natural hormone produced in the ovary of a female, with important roles in reproduction. The IUS is inserted into the uterine cavity and releases progestogen at a slow rate, which is the mechanism responsible for its action in protecting against pregnancy. It exhibits a contraceptive effectiveness of more than 99%.

The IUS has two long threads which are designed to hang out of the uterine cervix into the upper part of the vagina, after proper insertion. They can be felt by the woman herself by gently introducing a finger into the vagina, and serves to reassure that the device is in position.

The intrauterine device

An IUD is, on the other hand, a copper-containing plastic T-shaped device in which the copper is either in the stem or wound around the arms. Frameless IUDs are also available in which a thread is used to set the copper on the device. The device is introduced carefully into the uterus, and has two long threads, similar to the IUS, for the same purpose. In both devices, following insertion the threads are cut to the desired length so that they will not hang out of the vagina.


The IUS and the IUD are very different in many respects:

Mechanism of action

The IUS acts by releasing progesterone into the uterine cavity, which has the following actions:

  • Primary endometrial action - thinning and secretory atrophy of the uterine lining, making it unfavorable to implantation of the embryo even if fertilization occurs
  • Changing the characteristics of the cervical mucus so that it becomes and remains thick and tenacious, hostile to sperm penetration – the most immediate protective action of this device
  • Suppression of ovulation occurs in some women, by the inhibition of the natural gonadotropin-releasing hormone secretion which is responsible for the natural increase in LH and FSH gonadotropins, which trigger follicular development and ovulation
  • Decreased tubal motility and tubal ciliary function because of the action of progesterone may hinder sperm and ovum transport, as well as sperm capacitation
  • Ovum maturation may be affected by the abnormal hormonal milieu

The IUD acts by releasing copper ions into the uterine endometrium which renders it hostile to sperms, causing fragmentation and hindering their passage into the fallopian tubes to achieve fertilization. It also stimulates an inflammatory endometrial response which can destroy the embryo even if fertilization does occur.


Menstrual abnormalities

The IUS causes irregular menstruation, which may be light or heavy. Breakthrough bleeding is extremely common, as is the onset of amenorrhea within six to twelve months in half of all users. Those who continue to have menstrual bleeding may experience very short and light spotting. This type of bleeding is more common in the first few months. Dysmenorrhea usually subsides with an IUS, but may become worse in a few women.

The IUD may cause irregular intermenstrual bleeding, especially within the first few weeks. Later, however, many women report heavy and painful periods following IUD insertion. This is a major cause of discontinuation.


The IUS is more expensive than the IUD in most countries.

Other side-effects

The IUS may be associated with the following symptoms, especially in the first few months:

  • Headaches
  • Acne flares
  • Breast tenderness
  • Weight gain
  • Fluid retention
  • Ovarian follicular cysts

The IUD does not cause hormonal symptoms but may cause iron-deficiency anemia with related symptoms. It has no metabolic side-effects.

Endometrial effects

The IUS causes profound endometrial atrophy in many cases, while the IUD does not.


The IUS is contraindicated in women with current venous thromboembolism, and in women with current or a past history of cardiovascular disease, stroke, or breast cancer. Other contraindications include:

  • Cervical cancer
  • Liver cirrhosis or tumor
  • Irregular vaginal bleeding of unknown cause
  • Cerebrovascular disease
  • Untreated pelvic infection or sexually transmitted infection (STI)
  • Uterine or cervical abnormalities

The IUD is suitable for women with most medical conditions, but is contraindicated in women with:

  • Wilson’s disease
  • Active pelvic infection
  • Uterine or cervical abnormalities

Both the IUS and the IUD can give rise to serious pelvic infections if inserted into a woman with pre-existing STIs. For this reason, women undergo testing for chlamydia, gonorrhea (and other STIs at request) before insertion.

Duration of use

The IUS is licensed for five years, while the IUD can be left in for up to ten years.

Long-term complications

The use of the IUS is associated with a somewhat raised risk of breast cancer, but lower risk of endometrial and ovarian cancer. The IUD does not affect cancer risk.



Further Reading

Last Updated: Mar 16, 2023

Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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