ENDOMETRIUM AND WINDOW OF IMPLANTATION

Many women undergoing in-vitro fertilization (IVF) cycles of assisted fertilization fail to achieve pregnancy despite the fact that high morphological quality embryos have been transferred. This could be related to the fact that embryos are transferred to an uterus that is not yet ready to receive it.
The appropriate timing for embryo transfer is of fundamental importance for the success of the IVF treatment and must be determined within a time window, named “Window of Implantation or WOI”, in which the endometrium is in the so-called “receptive” stage, i.e. favorable to the acceptance and subsequent implantation of the embryo.
For most women, the optimal timing for embryo transfer is the same; for some women, however, the window of implantation may be displaced (i.e. it may occur slightly earlier or later than expected), thus leading to the transfer of the embryo to a non-receptive endometrium.
The lack of synchronization between an embryo ready for implantation and the endometrial receptivity stage is one of the main causes of repeated implantation failure (RIF) in IVF. Women with a clinical history of RIF may have a displaced window of implantation. Consequently, it is important to identify, in advance and accurately, the time window of “endometrial receptivity”, in order to improve the success rate of IVF treatments.