I found this on a website - part of an essay about coils:
Positional Abnormalities
Subtle positional abnormalities are best identified by HSG or ultrasound. After Essure placement, the device can migrate either proximally into the uterine cavity or distally through the distal tubes, sometimes being expelled into the peritoneal cavity [5]. To determine whether the microinserts are properly positioned, radiologists should identify the radiodense markers at both the proximal and distal ends of the device. The device's manufacturer has developed a grading system based on satisfactory (grade 2) or unsatisfactory (grades 1 and 3) position of the microinsert [5]. Grade 1 corresponds to expulsion of the device into the uterine cavity or proximal position of the device with more than 50% of the length of the inner coil trailing into the uterine cavity (Figs. 9A, 9B, 9C, 10A, 10B, 10C, 10D, 11A, 11B). Grade 2 is defined by a microinsert that crosses the uterotubal junction with less than 50% of the length of the inner coil trailing into the uterine cavity or when the proximal end of the inner coil is within 30 mm of the proximal fallopian tube measured from the contrast-filled uterine cornua (Fig. 3A, 3B). Grade 3 corresponds to a device that is too distal in the tube, with the proximal end of the inner coil more than 30 mm from the contrast agent?filled cornua (Figs. 12 and 13A, 13B), or when the device is expelled into the peritoneal cavity.
If the device is either grade 1 or 3 in position, one must assume that it is nonfunctional from a clinical standpoint, resulting from an abnormal or failed fibrotic reaction induced by the inner coil of the device (Figs. 13A, 13B and 14A, 14B). The abnormal reaction can manifest in nonocclusion or occlusion of the tubes only at their distal ends, neither of which ensures permanent contraception. Patients are instructed to continue using alternative contraception, have the devices repositioned, or opt for incisional sterilization.