Our results reveal that a refractory endometrium in a fertile woman produced by an IUD is induced by preventing the normal transition to a receptive gene expression profile through effects on a specific subset or cluster of genes that impact on endometrial receptivity.

A comparative randomized trial was made of two intrauterine contraceptive devices: Nova-T and MLCu375. The IUDs were used by 637 and 606 women, respectively, for one year, unless the device was removed earlier. The reasons for IUD removal were analyzed after one year using the life-table method. Statistically significant differences were found in expulsion and removal for bleeding and/or pain rates.

Nine hundred and seventy-four cavimetries were performed using Kurz's Cavimeter prior to the insertion of a MLCu375 IUD. In this trial, we studied the endometrial cavity length of these women. Results of the cavimetries were correlated to IUD complications to determine which uterine sizes were associated with IUD side-effects. The expulsion rate was higher for women with an endometrial cavity length equal to or greater than 45 mm (p < 0.01) for one and two years.

A comparative randomized study was made of three intrauterine contraceptive devices: the Nova-T, MLCu250 Short and MLCu375. An endometrial biopsy was performed on the 25th day of the menstrual cycle before and after IUD insertion. The tissue obtained was analyzed to determine estrogen and progesterone receptor concentration and endometrial morphology patterns in IUD users. Both estrogen and progesterone receptors decreased proportionally to the increased amount of copper in the IUD. The histologic study showed changes in endometria relative to the amount of copper, but these changes were transitory and disappeared after a year of IUD use.

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