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Understanding the IUD

Beverly Anderson and Mishka Terplan, MD, National Center for Health Research

The concept of the IUD (Intrauterine device) as a method to prevent

unplanned pregnancies has been around for a century. IUD technology

has advanced significantly since they were first introduced to Americans

in the 1920s, but the perception of other devices, such as the 1970’s

Dalkon Shield, leaves many women with outdated views about their safety

and effectiveness. More recent IUDs have an improved design that is a

safer and more effective form of birth control compared to older models. IUDs may be a good option for women looking for a long-term, alternative form of contraception. But before deciding if this option is right for you, it is important to understand the different types of IUDs, how they work, and the risks and benefits involved.

What is an IUD?

An intrauterine device (IUD) is a small, T-shaped piece of flexible plastic that is placed inside the uterus to prevent pregnancy. There are two types of IUDs available: hormonal (Mirena and Skyla) and copper (ParaGuard). The IUD is the most common form of reversible birth control in the world, used by about 100 million women. Although only 6% of reproductive-age women in the United States use IUDs, this number is quickly growing.[1], [2] In fact, it is the number one form of birth control used by gynecologists in the U.S. for their own birth control needs.[3]

How do IUDs work?

IUDs work to prevent pregnancy by several different mechanisms. It is important to understand that the IUD does not cause abortions. Rather, an IUD prevents pregnancy from occurring the first place.  Both types of IUDs physically interfere with sperm so it cannot reach the egg for fertilization.

The hormonal IUD releases a small amount of a synthetic hormone, progestogen, at a constant rate for several years.  This hormone is a progestin, and it very similar to the progesterone naturally produced by a woman’s ovaries each month. The progestogen sometimes prevents ovulation from occurring–in other words, an egg is not released from an ovary. Additionally, the progestogen thickens a woman’s cervical mucus and causes it to become sticky. If ovulation occurs and an egg is released, these changes help prevent pregnancy because 1) the thickened cervical wall blocks sperm from traveling to the site of fertilization and 2) the sticky uterine lining is a poor environment for an egg to implant and grow.[4]

The copper IUD contains no hormones.  It has a small copper wire wrapped around the plastic base of the device.  Its primary method of contraception is to physically block the sperm, because copper is also a natural spermicide.  The copper wire causes the uterus and fallopian tubes to produce a fluid that contains white blood cells, copper ions, enzymes, and prostaglandins. This combination is toxic to sperm. The combination of these factors makes the IUD an extremely effective method of birth control.

Who can get an IUD? How are they inserted?

Originally, IUDs were only prescribed to women who had at least one child. The insertion process was much easier and less painful for women who have already given birth, but recent improvements in the mechanisms of insertion have made IUDs available for all women. The Mirena IUD is not recommended for women who have had breast cancer within the past five years; however, the copper IUD is still safe for these women. Additionally, patients with an active, untreated, or recently treated sexually transmitted infection (STI) should not receive an IUD. However, individuals with a history of an STI can still get an IUD.

During the insertion process, a medical professional will sometimes administer a local anesthetic to reduce the pain associated with placing the IUD. This is usually not necessary for women who have given birth vaginally in the past. After insertion, it is important to periodically check the strings on the IUD that hang into the vagina to make sure it is still in place.  The strings are very thin, and will become softer over time. You should schedule a follow-up appointment with your physician four to six weeks after the IUD is placed for them to check the strings. The strings are rarely felt during intercourse.

What are the benefits to getting an IUD?

The biggest benefit to getting an IUD is that you don’t have to worry about birth control for 3 to 10 years, depending on the type of IUD. The manufactures of the Mirena IUD guarantee that the device lasts for up to five years, but research has suggested that it is effective for up to seven.[5], [6] The ParaGuard IUD lasts for at least ten years, and the newest IUD, Skyla, will last for three years. This option caters to women who have busy schedules or often forget to take their birth control pills on time.  Additionally, IUDs are extremely effective at preventing pregnancy. About 1-2 out of 1000 users will get pregnant while using an IUD within the first year.

There are specific benefits for each type of IUD as well. The progesterone in the hormonal IUD may reduce menstrual bleeding and cramping, as well as decrease your risk of anemia. The copper IUD can be used as a method of emergency contraception if it is inserted within five days after unprotected sex. Since the copper IUD contains no hormones, there is no risk of weight gain, mood changes, or other adverse reactions to increased progesterone levels.

The cost of an IUD can range from $500 to $1,000. This may seem like a high up-front cost, but when compared to birth control pills, which cost about $30 per month, an IUD is a cheaper method when used for more than two years. In fact, in a recent study that compared 15 different methods of contraception, the IUD proved to be the most cost-effective.

What are the disadvantages and risks of getting an IUD?

Neither type of IUD protects against sexually transmitted infections (STIs) or HIV. Additionally, both types of IUDs require a clinic visit for insertion and removal. Studies indicate that between 2 and 6% of the time, the IUD is rejected within the first year, and in some cases the woman doesn’t realize her IUD is no longer in place.[6] When the IUD falls out, this is called expulsion. Expulsion of the IUD can happen at any time, but is less common after it has been in place for a year. Expulsion of the IUD does not cause harm, but the patient is no longer protected from an unplanned pregnancy and a health care provider will have to re-insert the IUD.


However, if a woman has one expulsion, the chances of a second expulsion are much higher than the first time.

The copper IUDs can cause longer, heavier periods with the potential to cause anemia.  In more than 10% of patients, the hormonal IUD may cause irregular bleeding for 3-6 months following insertion, though regular periods may stop completely at this point. In more than 10% of patients, it can also cause ovarian cysts.[7] More than 5% of patients complain of each of the following complications: acne, headaches, pelvic pain, depressed mood or other symptoms that are similar to those for oral contraceptives.[7]

The most serious risk associated with getting an IUD is the potential for it to perforate (or puncture) the uterus at the time of placement. Although the chances of this occurring are reported to be only 1 in 1,000, it can require surgery to remove the IUD, and in rare cases the uterus must be removed, causing infertility.

Bottom Line


Overall, the IUD is an extremely effective and safe form of birth control for most women. It is cost-effective and requires very little thought after insertion. If you’re interested in getting an IUD, talk to your physician about your options!

All NCHR articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff. 


  1. Sonfield, Adam. “Popularity Disparity: Attitudes About the IUD in Europe and the United States.” Popularity Disparity: Attitudes About the IUD in Europe and the United States. N.p., July 2007. Web. June 2013.

  2. Grens, Kerry. “Most Women Misunderstand IUD Birth Control.” Reuters. Thomson Reuters, 21 Feb. 2013. Web. June 2013.

  3. Trussell, James. “Reducing Unintended Pregnancy in the United States.” Contraception Editorial January 2008. N.p., Jan. 2008. Web. June 2013.


  5. Healthwise Staff. “Intrauterine Device (IUD) for Birth Control.” HealthLinkBC. N.p., 2 July 2012. Web. June 2013.

  6. Canavan, Timmothy, MD. “Appropriate Use of the Intrauterine Device.” American Family Physician. Lancaster General Hospital, n.d. Web. July 2013.

  7. Newcomer C. for Cynthia Collins, Regulatory Review Officer, Division of Drug Marketing, Advertising, and Communication. Letter to Fadwa Almanakly, Associate Director, Advertising and Promotions, Bayer HealthCare Pharmaceuticals, December 30, 2009. http://

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