The chance of getting pregnant on the Mirena is Super slim, but like the ladies said.... anything is possible. I had mine for 2 years and for the first year I really liked it. Then all of the sudden I started gaining a ton of weight( I had been gaining the whole time I just didn't realize it until it got really bad), feeling exhausted all the time, sometimes very nauseous, sore breasts , so ridiculously moody...it seemed like every month around ovulation(it never prevented me from ovulating) I would gain several pounds and go through the motions of feeling very pregnant. I would take a test and it would come back neg. I was tested for thyroid issues, diabetes...you name it and it all came back negative. I suffered through this for several more months before I made the connection that all my symptoms had started when I got the Mirena and progressively got worse. So needless to say I had it taken out and things have gotten so much better. The weight that I gained is slowly coming off and I feel so much better emotionally and physically. Since having mine out I've heard of a lot of women who have had the same problems as me while on it. The more I think about the more I find that having something implanted in your body to prevent fertility is just not healthy.I know it seems so convenient but with possible problems that could develop it just doesn't seem worth it.