Ultrastructural development of the human decidua.

The ultrastructure of the human decidua in all three trimesters of normal pregnancy, in the tube in a case of ectopic pregnancy, and in hydatidiform mole is described. By Day 25 of the menstrual cycle, most of the ultrastructural characteristics associated with pregnancy have begun to appear: The morphologic manifestations of cellular activity in the true decidua are maximal by Day 70 of pregnancy. By Day 100, ultrastructural evidence of metabolic activity begins to decline. During the first 100 days of pregnancy, the ultrastructure of the stroma in the decidua capsularis is virtually identical with that in the decidua parietalis. Later in pregnancy, a material very similar to both basal lamina (basement membrane) and fibrinoid appears to be elaborated by the stromal cells. The decidual reaction in early tubal pregnancy is ultrastructurally indistinguishable from that in uterine pregnancy. The endometrial epithelial responses in normal uterine and tubal pregnancies also are similar. The reaction (Arias-Stella) appears to reflect hyperstimulation rather than degeneration and is further exaggerated in cases of hydatidiform mole. Previously undescribed ultrastructural features of the endometrial epithelium in the presence of a mole include intramitochondrial crystals and oval electron-rare intranuclear bodies with a fine fibrillar structure. Similar juxtanucleolar bodies are found in association with certain viral diseases.