Changes in uterine surface epithelium of rat during pregnancy

The first site of attachment of the trophoblast to the uterus in rodents is on the antimesometrial side and the inner cell mass is oriented mesometrially. The present study was performed with a view to study if comparable changes occur on both the mesometrial and antimesometrial side during early pregnancy in the rat using the scanning electron microscope. The results showed three types of ectoplasmic projections: namely, (i) a smooth surface and a narrow base; (ii) many folds and pits; and (iii) a ruffled surface and broad base, seen in clusters and located at intervals on the antimesometrial side only. The results suggest that these projections with ruffled surfaces may play a role in adhesion of the blastocyst and localisation of implantation sites in the rat.