Ovarian stimulation protocols: impact on oocyte and endometrial quality and function

Ovarian stimulation (OS) truly is an art. There exists a myriad of protocols used to achieve the same goal: stimulating the ovaries to produce more than one mature oocyte to improve the chance of a live birth. However, considerable debate remains as to whether OS impacts oocyte and endometrial quality to affect IVF outcomes. Whilst 'more is better' has long been considered the best approach for oocyte retrieval, this review challenges that notion by examining the influence of stimulation on oocyte quality. Likewise, improved outcomes following blastocyst transfer suggest OS perturbs endometrial preparation and/or receptivity, though correlating changes with implantation success remains a challenge. Therefore, the focus of this review is to summarise our current understanding of perturbations in human oocyte quality and endometrial function induced by exogenous hormone administration. We highlight the need for further research to identify more appropriate markers of oocyte developmental competence as well as those which define the roles of the endometrium in the success of ART.