My side effect resulted in pregnancy.. I had the mirena in for about 3 1/2 years with little side effects. Suddenly had about a 3 weeks period went to the doctors and she told me that was fine. Anyway months past and I started feeling sick and went to my general doctor and she told me i had IBS. Anyway a month or so later i go back to OBGYN and find out I am pregnant and not only that i was 22 weeks pregnant they showed me my daughter right there. IT was shocking.... I mean i accepted it and was kind of happy after but this didnt give me any time to prepare. My daughter was born about 18 weeks later healthy 8lbs 6 oz. Never did find that damn IUD.!!!!!