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Changes in the molecular organization of the plasma membrane of uterine epithelial cells during early pregnancy and, in particular, at the attachment period are reviewed. The review focuses on attachment in rodents but other species are also considered. Alterations in protein content and type, as determined with electrophoretic and freeze-fracture techniques, and an increase in tight junction complexity occur in several species. Ultrastructural histochemistry shows that glycocalyx carbohydrates of different species both increase and decrease depending on the type of carbohydrate. Changes in membrane cholesterol content also occur and recent studies showing major reorganization of the actin-containing membrane skeleton are reviewed to show the dynamism of this plasma membrane during the period of uterine receptivity for attachment of the blastocyst.

This paper reviews recent morphological work on peri-implantation endometrium collected from the Monash University In vitro Fertilization (IVF) Programme. Comparisons of endometrial tissue collected from women who had undergone different superovulation regimens demonstrated that significant structural differences could be detected by morphometry and ultrasound, but not by routine histopathology. Morphometric studies on endometrium from agonadal women receiving hormone replacement therapy demonstrated major differences between women with identical endocrine profiles. A biopsy inadvertently taken from one of these patients at the time of implantation was not of the appearance classically believed to be associated with receptivity for implantation. Studies have shown that the tight junction structure of endometrial epithelium is regulated during the menstrual cycle, suggesting that the integrity of the epithelial barrier may be important in the preparation of the endometrium for implantation.