Intrauterine Device

Mirena Intrauterine System (IUS)

Mirena is a hormone-releasing intrauterine device (or intrauterine system) placed in the uterus for birth control. Mirena is made of plastic and is T-shaped. It contains a synthetic hormone called levonorgestrel (LNG), a progestin hormone often used in oral contraceptive pills. Mirena releases the hormone into the uterus, and small amounts enter the blood stream. Two fine threads are attached to the stem of the T, which are used by a physician to remove the IUD. The IUD must be placed inside the uterus by a doctor, where it may remain for up to five years.

Mechanism of Mirena IUS

Mirena is termed an "intrauterine system" by the manufacturers because it has multiple mechanisms of action. The hormone in the IUD may sometimes stop the release of an egg from the ovary, but this is not the way it usually works as ovulation still occurs in most women. The Mirena system may prevent sperm from reaching or fertilizing an egg. However, some sperm may reach the egg anyway, resulting in fertilization. When fertilization does occur, Mirena is also thought to act as birth control by preventing the embryo from implanting in the uterus. It is not known which of these mechanisms is most important for preventing pregnancy and most likely all of them work together. All mechanisms of the IUD are not completely understood.

Effectiveness of Mirena IUS

The Minena Intrauterine System is thought to be very effective, with less than a 1% failure rate for perfect users. However, this number does not include women whose IUD fell out of place, which is a possible problem in the first few months after insertion. Mirena does not result in fertility problems for most users. After removing Minena, 20% of women trying to get pregnant were still unable to have a child a year after having Mirena removed. This is one reason that the manufacturers recommend Mirena only for women who have children.

Mirena IUS and Pregnancy

Because no method is 100% effective, some women using Mirena will become pregnant. When this happens, one possibility is a septic abortion (infection in the uterus while pregnant), which is a leading cause of maternal death around the world. If pregnancy should occur with a Mirena IUS in place, it should be removed. This removal process may result in a miscarriage. However, not removing the device also increases the risk of miscarriage, as well as infection, premature labor and premature delivery. When pregnancy continues with Mirena in the uterus, long-term effects on the unborn child are unknown. Because synthetic hormones are being released right into the uterus, birth defects, and infant health problems are a possibility.

Safety Information for Mirena IUS

Mirena does not protect against any sexually transmitted disease. Women who have pelvic-inflammatory disease (PID) must not use Mirena. Women who have more than one sexual partner or who are at risk for an STD are at a higher risk for PID, and should also not use Mirena. The Mirena IUD must not be used by any woman who is prone to infection. For example, women who have problems with their immune system, leukemia, AIDS, or intravenous drug abusers. It is also not suitable for women who might have cancer of the uterus or cervix, liver disease or liver tumor, or have breast cancer now or in the past.

Half of all pregnancies that occur to users of Mirena are ectopic (outside of the uterus), which can impair future fertility or even cause death. Therefore Mirena should not be used by anyone who has had an ectopic pregnancy or who is at high risk for ectopic pregnancy. It cannot be used by women with irregularly shaped uteruses or who have a condition of the uterus that distorts the uterine cavity, such as large fibroid tumors, or who have an allergy to the hormones in the device.

Side Effects & Health Risks of Mirena IUS

Common side-effects of the Mirena IUS include cramps, dizziness, or feeling faint while the IUD is being inserted. Sometimes, the cramping involves severe pain. Changes in menstrual bleeding are common. Women may have bleeding and spotting between periods, especially during the first few months. Sometimes the bleeding is heavier than usual, however, the bleeding usually becomes lighter than usual and may become irregular. Mirena makes the lining of the uterus thin, and this thinning causes lighter periods. Twenty percent of women completely stop having periods after using Mirena for a year.

One common problem experienced by Mirena users is the development of a cyst on the ovary. About 10% of women using Mirena will develop an ovarian cyst. These cysts may disappear on their own in a month or two. However, cysts can cause pain and sometimes will need surgery.

Some IUD users get a serious pelvic infection called pelvic-inflammatory disease (PID). PID is usually sexually transmitted, but can also be caused by germs entering the uterus during the insertion procedure. Women who have more than one sexual partner have a higher chance of getting PID. PID can cause serious problems such as infertility, ectopic (tubal) pregnancy, or constant pelvic pain. PID is usually treated with antibiotics. However, more serious cases of PID may require surgery. A hysterectomy (removal of the uterus) is sometimes needed. In rare cases, infections that start as PID can even cause death.

In rare cases is possible for Mirena to make a hole in the uterus. This is called perforation. If the uterus is perforated, it may require surgery to remove Mirena. Perforation can cause internal scarring (leading to infertility), infection (which can cause death), or damage to other organs (which can also cause death). A comprehensive list of possible side effects and health risks of the Mirena IUS are listed below.

Documented Health Risks for the Mirena IUS
Most Serious Most Common Less Common
  • Ectopic Pregnancy
  • Intrauterine Pregnancy
  • Sepsis (infection of the bloodstream)
  • Pelvic Inflammatory Disease (PID)
  • Irregular Bleeding
  • Amenorrhea (no periods)
  • Embedment (IUD stuck in uterus)
  • Perforation (IUD punctures uterus)
  • Ovarian Cysts
  • Breast Cancer
  • Death
  • Abdominal pain
  • Upper respiratory infection
  • Leukorrhea (vaginal discharge)
  • Nausea
  • Headache
  • Nervousness
  • Vaginitis (vaginal irritation)
  • Dysmenorrhea
  • Back pain
  • Weight gain
  • Breast pain
  • Skin disorder
  • Acne
  • Decreased libido (sex drive)
  • Depression
  • Abnormal Pap smear
  • Hypertension
  • Sinusitis
  • Failed insertion
  • Migraines
  • Vomiting
  • Anemia
  • Cervicitis (inflammation of the cervix)
  • Dyspareunia (pain during intercourse)
  • Hair loss
  • Eczema

Source: List taken from Mirena IUS manufacturer's doctors prescribing insert [download].

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The following links are provided as an informational resource or counterpoint and are not necessarily endorsed by the author:

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