1. Women using a progesterone-releasing IUD for birth control had significantly fewer unintended pregnancies, including ectopics, compared to those using a copper IUD.
2. From a clinical perspective, both forms were highly effective, with failure rates of <1%.
Evidence Rating Level: 1 (Excellent)
Study Rundown: The intrauterine device (IUD) is the most effective form of reversible birth control currently on the market. Two IUD types are currently available—a progesterone releasing system (commercially known as the Mirena) and a copper IUD (Paragard in the U.S., although generics of various types are available in Europe). Both are known to be highly effective with failure rates for ranging from 0.1-0.6% for the hormonal IUD and ranging from 0.1-2.2% for the copper IUD; however, few studies have directly compared the effectiveness of the two IUDs. In this large-scale, multinational study, researchers compared rates of unintended pregnancy after one year in women using the two devices.
Both the copper and the hormonal IUD were found to be highly effective, with failure rates of <1%. However, when directly compared, the hormonal IUD was associated with a significantly lower risk of pregnancy after one year, including ectopic pregnancy, than the copper IUD.
Strengths of this study included the rigorous prospective cohort design, large sample size, and minimal loss to follow-up (2.0%). One limitation was that more than 30 types of copper IUDs were accepted into the study, including those of different sizes, which could have had varying levels of effectiveness. Additionally, they did not collect data on concurrent use of other contraception (e.g. male or female condoms, diaphragm, morning after pill), which could have differed between the cohorts. Future studies that randomized women to receive one type of copper IUD or a hormonal IUD and controlled for additional contraceptive use would further support these findings.
In-Depth [Prospective Cohort]: Researchers recruited 61 448 women with newly inserted IUDs from 6 European countries during 2006-2012. Participants and their physicians filled out a baseline survey and a follow-up questionnaire at 12 months. The primary outcome was pregnancy, including ectopic. Of the 58 324 women included in the final analysis, 41 001 (70%) had a levonorgestrel hormone releasing IUD (LNG IUD) and 17 323 (30%) had a copper IUD.
A total of 118 unintended pregnancies occurred during the study period, 26 in the LNG IUD users and 92 in copper IUD users. The failure rate for the LNG IUD cohort was significantly lower than the copper IUD (0.06 pregnancies per 100 woman-years vs. 0.52, aHR=0.16, 95% CI=0.10-0.25). The women in the LNG IUD cohort were also less likely to have an ectopic pregnancy (0.02 pregnancies per 100 woman-years vs. 0.08, aHR=0.26, 95% CI=0.10-0.66).
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