This study was supported by grants from the Susan Thompson Buffett Foundation. Duramed Pharmaceuticals (now Teva Pharmaceuticals) donated the copper IUDs for this study. Dr. Bednarek reported ties to Bayer HealthCare Pharmaceuticals (maker of Mirena IUDs), Schering Plough (now merged with Merck), and Medicines 360 (a not-for-profit pharmaceutical company); her associates reported ties to Merck, Medicines 360, Duramed, Teva Women's Health Research, and others.