Epithelial lining of the endometrium during the luteal phase in patients under controlled ovarian hyperstimulation

The endometrium is receptive for the embryo and presents an implantation window for a limited time. This study is aimed at highlighting an alternation in pinopod expression and to provide more analysis of the structural characteristics of epithelial lining of the endometrium during luteal phase in patients undergoing controlled ovarian hyperstimmulation (COH). Twelve oocyte donors were used. They underwent two endometrial biopsies 2-7 days after human chronic gonadotrophin (HCG) administration. Endometrial epithelial surface appearance was evaluated by scanning electron microscopy. Microvilli became more uniformly distributed as the luteal phase progressed. Also the central aspects of the cells appeared to protrude more into the endometrial lumen as the cycle progressed. Apical protrusions (pinopods) were noted to develop and regress during the midluteal phase after HCG administration. Pinopods began development in the region of the glandular orifices to become much denser at the glandular orifices than in regions further away from the glands. In conclusion, epithelial lining of endometrium in stimulated cycle during the luteal phase progresses in an orderly manner. This advanced development may result in an alteration of the window of implantation between the developing endometrium and the developing blastocyst and affect pregnancy rates in women undergoing controlled ovarian hyperstimmulation.