Study Objective: To identify factors that might contribute to pregnancies reported after hysteroscopic sterilization worldwide. Design: Retrospective review of commercial data compiled from the MAUDE database, medical literature, and manufacturer reports received during commercial distribution of hysteroscopic sterilization micro-inserts from 2001 through 2010 (Canadian Taskforce classification ill descriptive study). Measurements and Main Results: From 2001 through 2010, 497 305 hysteroscopic sterilization kits were distributed worldwide, and 748 pregnancies were reported, i.e., 0.15% of the estimated user population based on the number of distributed kits. The data were sufficient to enable analysis of 508 pregnancies for potential contributing factors and showed most to be associated with patient or physician noncompliance (n = 264) or misinterpreted confirmation tests (n = 212). Conceptions deemed to have occurred within 2 weeks of the procedure and therefore too early for detection were identified in 32 cases. Conclusion: Although there are limitations to the dataset and the study design is retrospective, it represents the largest body of cumulative hysterosdopic sterilization data available to date. Of the 748 pregnancies reported, it is apparent that some might have been prevented with greater patient and clinician attention to interim contraceptive use and counseling and with more rigorous evaluation and informed interpretation of the procedure confirmation tests. Although the estimated pregnancy rate based on such a dataset is likely an underestimation, it does suggest that the evaluable field performance of hysteroscopic sterilization micro-inserts is consistent with the labeled age-adjusted effectiveness of 99.74% at 5 years. (c) 2014 AAGL. All rights reserved.