The role of endometrium in implantation.

As implantation approaches the different endometrial components demonstrate certain anatomical and molecular changes. Molecules with an effect on uterine receptivity for blastocyst implantation include integrins, leukaemia inhibitory factor (LIF), interleukin-1 (IL-1) and colony stimulating factor-1 (CSF-1). Although over the past 5 years our understanding of the implantation process has improved dramatically, there are still many unanswered questions. Undisputed morphological, biochemical and molecular markers of uterine receptivity that permit quantification of the human implantation window are still unknown. The factors which regulate the expression of integrins, LIF, CSF-1 and IL-1, the mode of action of these molecules and their role in human implantation remain unclear. Only when these questions are answered shall we be able to apply the molecular aspects of implantation to clinical practice.