Contraceptive efficacy and safety of the 52-mg levonorgestrel intrauterine system for up to 8 years: findings from the Mirena Extension Trial

Background: The 52-mg levonorgestrel-releasing intrauterine system is an established, long-acting contraceptive option with approved use for up to 7 years.

Objective: The Mirena Extension Trial evaluated the efficacy and safety of the 52-mg levonorgestrel-releasing intrauterine system during extended use beyond 5 and up to 8 years.

Study design: This was a multicenter, single-arm study in the United States, enrolling existing users of the 52-mg levonorgestrel-releasing intrauterine system, aged 18 to 35 years, who have had the system for 4.5 to 5 years. We assessed the contraceptive efficacy (Pearl Index) and cumulative failure rate (using the Kaplan-Meier method) of the 52-mg levonorgestrel-releasing intrauterine system during extended use. We also evaluated bleeding outcomes and adverse events.

Results: Of the 362 participants starting year 6, 243 entered and 223 completed 8 years of 52-mg levonorgestrel-releasing intrauterine system use. Just more than half the participants were parous. The mean (standard deviation) age was 29.2 (±2.9) years, and all participants were aged ≤36 years at the end of year 8. Two pregnancies occurred, both with the device in situ. The year 6 pregnancy was of undetermined location and resolved spontaneously. The pregnancy in year 7 was ectopic and resolved with methotrexate treatment. In both cases, the 52-mg levonorgestrel-releasing intrauterine system was removed and the participants left the trial. For years 6 to 8, the 3-year Pearl Index (95% confidence interval) was 0.28 (0.03-1.00) with a 3-year cumulative failure rate of 0.68% (0.17-2.71). Pearl Indexes for years 6, 7, and 8 were 0.34 (0.01-1.88), 0.40 (0.01-2.25), and 0.00 (0.00-1.90), respectively. The 3-year (years 6-8) ectopic pregnancy Pearl Index was 0.14 (0.00-0.77). We found treatment-emergent adverse events in 249 of 362 participants (68.8%), with 65 (18.0%) events considered to be related to the 52-mg levonorgestrel-releasing intrauterine system. The discontinuation rate was 38.4% (139/362), most commonly because of desire for pregnancy (12.2%, 44/362). During extended use beyond 5 years and up to 8 years, participants reported a decrease in the mean number of bleeding or spotting days with approximately half of the women experiencing amenorrhea or infrequent bleeding. We did not enroll a sufficient number of women using the 52-mg levonorgestrel-releasing intrauterine system for contraception and heavy menstrual bleeding to assess extended use for that indication. At the end of year 8, most (98.7%, 220/223) of the participants who completed the study remained satisfied with the continued use of the 52-mg levonorgestrel-releasing intrauterine system. Of the 31 women who discontinued early because of desire for pregnancy with evaluable data for return-to-fertility analysis, 24 reported a posttreatment pregnancy within 1 year, giving a 12-month return-to-fertility rate of 77.4%.

Conclusion: The 52-mg levonorgestrel-releasing intrauterine system, initially approved for 5 years, maintains high contraceptive efficacy, user satisfaction, and a favorable safety profile through 8 years of use. Participants reported 26 posttreatment pregnancies in total, of which 24 occurred in women who had discontinued the 52-mg levonorgestrel-releasing intrauterine system because of a desire for pregnancy. Of note, among women who elected to continue use through 8 years, bleeding patterns remained highly favorable. These findings support continued 52-mg levonorgestrel-releasing intrauterine system use for up to 8 years in women who wish to continue treatment.