[The histological reaction of the endometrium to gestagens applied locally]

To study the histologic changes produced by a new type of progesterone-medicated intrauterine device we examined the endometria of six hysterectomy specimens and one complete curettage. After being in place for 1 month the device induced a mild perifocal "arrested secretion" of the upper layers of the endometrium; after 3 months the change was pronounced, with decidually transformed stromal cells and atrophic glands. After 12 months these changes had partially progressed to fibrous atrophy. The endometrium underlying the perifocal-arrested secretion showed either proliferative or secretory changes almost like those of the lower functionalis of a normal menstrual cycle. A generalized atrophy of glands developed only when the patient had used oral contraceptive agents before the device was inserted. The perifocal arrested secretion thus differs from the generalized arrested secretion of the endometrium that follows use of oral or injected gestagens and from the decidualization produced mechanically by the local effect of an intrauterine device. The contraceptive effectiveness of the medicated intrauterine device, as compared with that of a simple device, is increased by the glandular atrophy of the arrested secretion. It avoids the dangers of the generalized effects of progestational agents by limiting the changes to the upper layers of the endometrium which are so important for implantation.