Contribution to the physiology and pathology of endometrial receptivity: the determination of protein patterns in human uterine secretions

In this study, the uterine protein patterns of greater than 200 patients of the sterility treatment programme of the Department of Obstetrics and Gynaecology, University of Ulm were analysed by the technique of uterine secretion electrophoresis (USE) of minute quantities. These analyses reveal three protein patterns, typical for the equivalent phases of the menstrual cycle: intermediate phase-, proliferative phase- and secretory phase. There appear up to 63 protein bands, most of which represent proteins less than 68 kd. Those separation areas below 68kd show characteristic 'families' of protein bands, which typically constitute the three phase patterns. As a result of our study, a secretory phase pattern lasting 10 days is demonstrated, suggesting a remarkably long 'receptive phase' for the initiation of implantation. The fully expressed secretory phase pattern appears from day 15 to day 25 of the ideal menstrual cycle (28 days length). The 'implantation window' of the endometrium seems to remain open for a surprisingly long period of time. This insight sheds light on the success of embryo transfer after IVF when the cleavage stage embryo arrives in the uterine cavity several days earlier than after normal fertilization. Such early exposure to the uterine milieu nevertheless does not preclude implantation.