Although intrauterine devices (IUDS) are the most widely used form of irreversible contraception worldwide, they are an underutilized contraceptive method in the United States. (115).

Mechanism of action: There are two types of IUDs currently available in the U.S.: a copper IUD (Paraguard®) and a progestin-impregnated progestin intrauterine system (IUS), Mirena®. Both medicated and nonmedicated intrauterine devices (IUDs) have multiple mechanisms of action that provide for contraceptive protection. Both medicated and nonmedicated IUDs can alter the uterine lining so that it becomes unfavorable for implantation. Release of copper ions also alters fluid in the uterine cavity in a manner that impairs the viability of sperm, thereby inhibiting fertilization. This mechanism may be responsible for the high efficacy of copper IUDs as emergency contraception.

IUDs can also alter both sperm motility and integrity (116-119). Medicated, or hormonal IUDs, can interfere with sperm motility by thickening cervical mucus. Sperm head-tail disruption has been reported in the presence of a copper IUD (116). IUDs, whether hormonal or non-hormonal, do not provide protection against sexually transmitted diseases. However, it is important to recognize that IUDs do not cause PID (120, 121), and that the historical associations that both physicians and the lay public maintain between IUDs and PID/tubal infertility are false.

Timing of IUD insertion: The IUD can be inserted at any point in the cycle as long as the patient is not pregnant. An IUD can be inserted immediately postpartum, post abortion, or as an 'interval' insertion. However, the progestin IUS, Mirena®, is generally inserted in the first five days after menses because this is how the clinical trials were performed, and it is not known if Mirena® has the same post-coital contraceptive effects as the copper IUD (Mirena® should not be used as an emergency contraceptive).

Interval Insertion: An 'interval' insertion is defined as insertion in women who are neither postpartum nor post abortion, or an insertion in women 6 weeks after delivery (122). Traditionally, physicians were taught that the best time for IUD insertion was either during menses or immediately after menstruation. Limiting insertion to these time points, however, created a barrier to their use. Data now suggest that IUD insertion between cycle days 12 to 17 results in greater IUD continuation rates. The Centers for Disease Control and Prevention reviewed data from more than 9,000 copper T-200 IUD insertions and found that IUDs placed after cycle day 11 resulted in fewer IUD removals during the first 2 months of IUD use. Insertions after day 17 resulted in more frequent IUD removal due to pain, bleeding, or accidental pregnancy (123).

Progestin-only IUD: The levonorgestrel intrauterine system (Mirena LNG IUS) releases 15mcg of levonorgestrel per day from a polymer cylinder mounted on a T-shaped frame containing 52mg levonorgestrel; it is covered by a rate-releasing controlling membrane. It is approved for 5 years of use. The failure rate is low: 0.16 per 100 woman years of use. Its mechanisms of action include production of an atrophic and inactive endometrium, disturbed ovulation, and thickening of the cervical mucus. Ovulation may be inhibited in some women, but this is not the main mechanism of action. Both the volume of menstrual flow and the number of days of bleeding are reduced (124). The mean number of bleeding and spotting days is initially increased but in 3-6 months' time, the number of bleeding and spotting days is similar to users of the copper-IUD. During the first year of use, about 20% of women will be become amenorrheic (124). A recent meta-analysis of randomized controlled trials reveal that LNG IUS users were significantly more likely than all other IUD users to discontinue its use because of hormonal side effects and amenorrhea (125), so appropriate counseling is an important component of success. Initial irregular spotting or bleeding, and hormonal side effects like acne and ovarian cysts may occur in some users. In part because there is no user-dependence, the LNG IUS offers improved effectiveness over other hormonal methods (125).

Non Contraceptive uses of LNG IUS: Multiple descriptive studies and clinical trials have been performed on the non contraceptive benefits of the Levonorgestrel IUS (LNG-IUS) (126-132).

One such study evaluated the efficacy and performance of the LNG-IUS in 44 women with menorrhagia after medical therapy had failed. (132) At 12 months, 79.5% of participants continued use of the LNG-IUS. After LNG-IUS insertion, the most common bleeding pattern at 3 months was spotting followed predominantly by amenorrhea or oligomenorrhea at 6, 9, and 12 months. Hemoglobin levels significantly increased from 102 g/L before insertion to 128 g/L at 12 months (p<0.01).

The LNG-IUS is an effective treatment for menorrhagia It remains unclear if the LNG-IUS is effective in reducing menstrual blood loss in women with menorrhagia due to the presence of intramural or subserosal fibroids.

Another prospective study observed that the 20mcg LNG-IUS provides effective protection against endometrial hyperplasia in post-menopausal women on estrogen replacement therapy (in the daily dose of 2mg of estradiol valerate).