My OB also did not spend time discussing this side effect. I had my Mirena inserted about 8 weeks post partum. It was very painful - and the first one did not go in correctly, so she had to take it out and try again. After a few days of discomfort and about a week of bleeding (which I thought was normal) everything seemed fine. At my next visit the doctor could not find the string, so scheduled an ultrasound, but still no Mirena! Then came the radiograph. Surprise, it was in there - they just could not tell where. They then scheduled a laparoscopy to remove it. They said it could turn into a laparotomy if they could not get it with the scope. Of course they didn't get it, couldn't even find it with the scope. So they made an incision below my belly button around where a c-section incision would be and then found the Mirena towards the bottom of my uterus embedded in the ligament. She said it was hard to get to, and had to be dissected out. It was very painful post op and took a while to recover from. It has been over 5 weeks, and I am still not 100%. I just thought I should share my story so people will know it is a possibility!