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The Mirena 52-mg levonorgestrel intrauterine system (IUS) is highly effective for preventing pregnancy. Originally approved for 5 years of use, it has since demonstrated contraceptive efficacy beyond this period in clinical trials. In this multicenter U.S. study, 362 women (mean age, 29; ≈50% nulliparous) nearing 5 years of Mirena IUS use were followed prospectively for 3 additional years.
During years 6 through 8 of Mirena IUS use:
Two pregnancies occurred, resulting in a cumulative contraceptive failure rate of 0.68%.
The Pearl index (commonly used to compare failure rates of contraceptive options) was 0.28 pregnancies per 100 women-years of contraceptive use, similar to the Pearl index for 5 years of Mirena IUS (i.e., 0.2). The copper intra…