HONOLULU (FRONTLINE MEDICAL NEWS) – The risk of unintended pregnancy was 84% lower with use of levonorgestrel-releasing intrauterine devices than with copper intrauterine devices, according to an analysis of secondary outcomes in a prospective international cohort study of 61,448 women.

EURAS-IUD (the European Active Surveillance Study for Intrauterine Devices) reported its primary outcome in early 2014, showing very low and similar uterine perforation rates in women receiving either levonorgestrel-releasing IUDs or copper IUDs for the first time.

Among secondary outcomes, the levonorgestrel-releasing IUD (Mirena) was associated with a significantly lower risk of unintended pregnancy than were copper IUDs, after adjustment for the influence of age, body mass index, and parity, Dr. Klaas Heinemann Jr. and his associates reported at the annual meeting of the American Society for Reproductive Medicine.

The risk of ectopic pregnancy also was lower with the Mirena than with copper IUDs, showing a 74% decrease in the likelihood of ectopic pregnancy after adjustment for the effects of age, body mass index, and parity, said Dr. Heinemann of the Berlin Center for Epidemiology and Health Research.

Rates of unintended or ectopic pregnancies were very low in both groups.

Among the 43,078 women receiving the Mirena, follow-up information on 41,001 women aged 18-50 years provided data on 44,633 women-years of observation. Among the 18,370 women receiving copper IUDs, follow-up information on 17,323 women aged 18-50 years provided data on 17,703 women-years of observation.

The 26 contraceptive failures on the Mirena included 13 in women with unrecognized expulsion of the IUD and 1 with a dislocated IUD. The 92 contraceptive failures on copper IUDs included 16 women with unrecognized expulsion of the IUD and 26 with a dislocated IUD.

On the Pearl Index of contraception effectiveness (the number of unintended pregnancies divided by 100 women-years), the Mirena rated 0.06 and copper IUDs rated 0.52, Dr. Heinemann reported. Pregnancy incidence rates were less than 0.08/100 women-years with the Mirena and less than 0.56/100 women-years with copper IUDs.

The lower pregnancy rate with the Mirena was present in all age groups, he added.

Seven confirmed ectopic pregnancies in the Mirena group and 14 in the copper IUD group produced incidence rates of less than 0.05/100 women-years with the Mirena and less than 0.10/100 women-years with copper IUDs.

The 70% of women who received the Mirena tended to be older (mean age, 37 years) than those who got copper IUDs (mean age, 33 years). The women who got the Mirena also were less likely to have delivered a child within the prior year (20%) or to be breast-feeding at the time of insertion (9%), compared with women who got copper IUDs (29% and 15%, respectively).

The research was funded by Bayer, which markets Mirena. Dr. Heinemann is a former employee of Bayer Schering Pharma.

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