Figure 10.5 Levonorgestrel T (Mirena™) intrauterine device.
The levonorgestrel in the T device is much more potent than natural progesterone and has a strong effect on the endometrium. The hormone is released at an initial rate of 20 μg daily, which declines to half this rate by 5 years. Blood hormone levels are significantly lower than with other progesterone-only contraception and remain stable at approximately 150 to 200 pg/mL (61). About 85% of cycles are ovulatory. The contraceptive effect of the levonorgestrel intrauterine device is a result of thickened and scant cervical mucus, endometrial atrophy, and an intrauterine inﬂammatory response (62).
The IUD is not an abortifacient. The contraceptive effectiveness does not depend on interference with implantation, although this phenomenon occurs and is the basis for using copper IUDs for emergency contraception. Sperm can be obtained by laparoscopy in washings from the fallopian tubes of control women at midcycle; fewer sperm are present in the tubal washings from women wearing IUDs (63). Ova ﬂushed from the tubes at tubal sterilization showed no evidence of fertilization in women wearing IUDs (64). Studies of serum β-human chorionic gonadotropin (β-HCG) levels in women wearing IUDs do not indicate pregnancy (65).
The copper T380A and the levonorgestrel T have remarkably low pregnancy rates, less than 0.2 per 100 woman-years. Total pregnancies over a 7-year period were only 1.1 per 100 for the levonorgestrel T and 1.4 for the copper T380A (58). Twelve-year data on the copper T380A showed a cumulative pregnancy rate of only 1.9 per 100 women and no pregnancies at all after year 8 (66).
Modern IUDs provide excellent contraception without continued effort by the user. Both the copper T380A and the levonorgestrel T protect against ectopic pregnancy. The levonorgestrel T, by releasing levonorgestrel, reduces menstrual bleeding and cramping. It is used extensively to treat heavy menstrual bleeding and is used in Europe and the United Kingdom as an alternative to hysterectomy for menorrhagia (67). The levonorgestrel T also has a beneficial effect on menorrhagia from uterine fibroids; the benefit may be diminished with distorting submucosal fibroids (68,69). The levonorgestrel T is an effective way to deliver the necessary progestin therapy in postmenopausal women on estrogen therapy (70). Additional noncontraceptive benefits include a reduced risk of endometrial cancer and improvement in symptoms of endometriosis and adenomyosis (71–74).
Infection The Women’s Health Study found the Dalkon Shield device (now withdrawn from the market) to increase the risk of PID eightfold when women hospitalized for PID were compared with control women hospitalized for other illnesses (75). In contrast, risk from the other IUDs was markedly less. Increased risk was detectable only within 4 months of insertion of the IUD. A prospective World Health Organization study revealed that PID increased only during the first 20 days after insertion. Thereafter, the rate of diagnosis of PID was about 1.6 cases per 1,000 women per year, the same as in the general population (76).