A study presented at the Society For Family Planning’s December 2022 meeting the researchers looked at hormone release levels from the Mirena IUD, as well as pregnancy rates, and bleeding.
The Mirena IUD contains levonorgestrel that is significant for the contraceptive protection and the control of menstrual periods.
The device has a trough in the center which gradually releases the hormone, which then can find it’s way into the blood stream.
In the first year the hormone level is leaks from the device most effectively and the blood levels are approximately 20 mcg per day.
The early device approval was for just 5 years of use. Current studies show that in year 8 the device is still producing about 6.5 mcg per day.
Just to contrast the Skyla device which is approved for 3 years of has a blood level of about 5 mcg in the third year. Which makes some gynecologists feel they would be able to still have patients be protected against pregnancy in year 9 and 10, but we have no data to prove this.
About 60% of women will find they have more bleeding or spotting in years 7 and 8 of the device. This may not mean more risk of pregnancy for those who aren’t bothered by this and want to keep their device, but for women looking for cycle control, they will have to consider their bleeding patterns when deciding when to change their IUD.
