Two years’ experience with two levonorgestrel-releasing intrauterine devices and one copper-releasing intrauterine device: a randomized comparative performance study**This work was undertaken as part of the contraceptive development programs sponsored and coordinated by the International Committee for Contraception Research and the Population Council, New York, New York. Financial support was provided by the International Development Research Center of Canada, the Ford Foundation, and the Rockefeller Foundation, New York, New York.