[Histological reaction of the endometrium to intrauterine administered gestagens].

The effects of a progesterone-releasing IUD on endometrial histology were studied in 6 uteri removed for medical reasons and in 1 case in which complete curettage was performed. Within 3 months of insertion, 2 layers of endometrial tissue were easily distinguished: an upper layer of predecidual or decidual stroma cells, similar to that observed when gestagens are given orally; and a lower layer of proliferating endometrium, corresponding to the stage of the cycle. 12 months after insertion the decidual development of the stroma approached a fibrous atrophy. The mechanism of action of the progesterone-releasing IUD depends on the mechanical decidualization of the endometrium and the glanduar atrophy due to the gestagen. The device avoids the dangers of generalized hormone exposure and leaves the basal layer of endometrium capable of regeneration.