The blastocyst and the endometrium are in a constant state of cross-talk. In order for successful implantation to take place, the blastocyst must be at the appropriate stage of development, and needs to signal a well synchronized endometrium  to ‘accept it”. This dialogue between embryo and endometrium involves growth factors, cytokines, immunologic accommodations, cell adhesion molecules, and transcription factors. These are all mostly genetically driven but are also heavily influenced by numerous physiologic, pathophysiologic, hormonal and molecular mechanisms capable of profoundly affecting the receptivity of the secretory endometrium to the overtures made by the embryo, to implant.

Embryo implantation takes place 6-9 days after ovulation. This period is commonly referred to as the “window of implantation (WOI)”. In the past it was believed that as long as the embryo reached the uterus in this 4 day time frame, its chance of implanting would not be affected.

In 2013, after evaluating 238 genes in the secretory endometrium and applying bioformatics, Ruiz-Alonzo, et all introduced the Endometrial Receptivity Array (ERA) . Using this test, they categorized mid-secretory endometria into 4 categories: “a) proliferative, b) pre-receptive, c) receptive or d) post-receptive”. They claimed that women with pre-receptive or post-receptive endometria were more likely to experience failed implantation post-embryo transfer (ET). It was in large part this research which suggested that the concept of a relatively “wide” (4day) WOI, was flawed, that an optimal WOI is likely much narrower and could be a critical factor in determining the success or failure of implantation post-ET. Ruiz-Alonzo also  reported that about 25% of women with recurrent IVF failure (RIF), have pre, or post-receptive endometria. They presented data suggesting that  viable IVF pregnancy rates could be enhanced, by deferring FET by about 24 hours in women who had pre-receptive endometria and bringing ET forward by the same amount of time, in women with post-receptive endometria,   There is no doubt that ERA testing has opened the door to an intriguing arena for research. Presently however, available data is inconclusive. Here, following  recent studies are 2 dissenting opinions regarding  the value for ERA:

• Basil and Casper (2018) state: “Performing the ERA test in a mock cycle prior to a FET does not seem to improve the ongoing pregnancy rate in good prognosis patients. Further large prospective studies are needed to elucidate the role of ERA testing in both good prognosis patients and in patients with recurrent implantation failure”
• Churchill and Comstock (2017)  conclude:” In our preliminary observations, the non-receptive ERA group had similar live birth rates compared to the receptive ERA group. It appears the majority of the pregnancies conceived in the non-receptive group occurred during ovulatory cycles and thus a non-receptive ERA in a medicated cycle likely does not have prognostic value for ovulatory cycles. Larger studies are needed to assess the prognostic value of ERA testing in the gen-eral infertility population.”

There are additional negatives that relate to the considerable emotional and financial cost of doing ERA testing:

1. First, the process costs $600-$1000 to undertake
2. , Second, it requires that the patient undergo egg retrieval, vitrify (cryobank) all blastocysts, res for 1 or more cycles to allow their hormonal equilibrium to restore, do an ERA biopsy to determine the synchronicity of the endometrium, wait a few weeks for the results of the test and thereupon engage in undertaking an additional natural or hormonal preparation cycle for timed FET. This represents a significant time lapse, emotional cost and additional expense.

Presently, ERA testing is only advocated for women who have experienced several IVF failures. However, some authorities are beginning to advocate that it become routine for women undergoing all IVF. The  additional financial cost inherent in the performance of the ERA test ($600-$1000), the considerable time delay in getting results, the fact that awaiting results of testing and preparing the patient for FET, of necessity extends the completion of the IVF/ET process by at least a few months, all serve to increase the emotional and financial hardship confronting patients undergoing ERA. Such considerations, coupled with the current absence of conclusive data that confirm efficacy, are arguments against the widespread use of ERA . In my opinion, ERA testing should presently be considered as being  one additional diagnostic and be confined to women with “unexplained” RIF. Gold standard statistical analyses require that all confounding variables be controlled while examining the effect of altering the one under assessment. There is an obvious interplay of numerous, ever changing variables involved in outcome following ET,  e.g. embryo competency, anatomical configuration of the uterus and the contour of the endometrial cavity, endometrial thickness, immunologic and molecular factors as well as the very important  effect of technical skill/expertise in performing the  ET procedure …(to mention but a few). It follows that it is virtually impossible to draw reliable conclusions from IVF-related randomized controlled studies that use outcome as the end-point. This applies equally to results reported following “ gold standard”  testing on the efficacy of ERA and, is one of the main reasons why I question the reliability of reported data (positive or negative). The fact is that IVF (and related technologies) constitute neither a “pure science” nor a “pure art”. Rather they represent an “art-science blend”, where scientific principles applied to longitudinal experience and technical expertise coalesce to produce a biomedical product that will invariably differ (to a greater or lesser degree) from one set of clinical circumstances to another. Since, the ultimate goal of applied Assisted Reproductive Medicine is to safely achieve the birth of a viable and healthy baby, the tools we apply, that are aimed at achieving this end-point, are honed through the adaptation of scientific principles and concepts, experience and expertise, examined and tested longitudinally over time. Needless to say, the  entire IVF/ET process is of necessity subject to change and adaptation as new scientific and technical developments emerge. This absolutely applies to the ERA as well!