Fine Structural Effects of Intrauterine Contraceptives on the Human Endometrium

Abstract

Of 198 endometrial biopsies performed on 82 women with Lippes loops in situ for 6 weeks to 40 months 124 were proliferative and 74 were secretory. Samples were obtained from immediately beneath the device between the loops and from areas remote from the device. Specimens of basal endometrium lower segment or endocervix were excluded. Control tissue was obtained before insertion of the device. Slides were prepared for electron microscopy. No consistent generalized pathologic change was observed in either proliferative or secretory endometria. The stroma immediately beneath the loop appeared compressed and fibrotic throughout the cycle. Proliferative epithelium maintained the normal pattern of juxtaposed light and dark (electron-dense) cells mitotic activity and distribution of microvilli and cilia. No progression of epithelial ultrastructural differences occurrred after their first appearance in the second month after IUD insertion. Precocious changes in epithelial ultrastructure included 1) the appearance of a nucleolar channel system normally considered indicative of ovulation or exogenously administered hormones in 15-29% of endometria judged to be preovulatory; 2) numerous large mitochondria usually associated with the postovulatory phase in the late-proliferative endometrium and occasionally as early as in the midproliferative; and 3) the development of confluent fields of glycogen at the end of the proliferative phase a few days earlier than in controls. The premenstrual endometrium resembled the contrl of this stage; scarcity of microvilli and other characteristic ultrastructural traits of regression were noted. Ultrastructural changes in the proliferative stroma were observed first about 1 day preovulatory when the cytoplasm appeared better differentiated than in the controls. The stromal cells were highly differentiated at the end of the first postovulatory week; the cytoplasmic complexity at Days 19 or 20 often resembled that of Day 25 controls. Premature and asynchronous development of the endometrium may affect the correlation with ovular development which is a prerequisite for normal implantation. Since the IUD creates an unfavorable environment for blastocystic attachment but does not dislodge the implanted ovum its action is considered contraceptive rather than abortifacient in the usual sense.