ERA test in IVF programs – how, when, and why?

ERA test, which stands for Endometrial Receptivity Analysis, was a test that showed promise in its early stages because it was supposed to help identify the window of implantation when the embryo is most receptive. Unfortunately, after many years of research, the results of this test have not proven to increase the live birth rate, which is the primary outcome of interest. Consequently, we have almost abandoned this test and do not recommend its use. If it is deemed necessary, it should only be performed in patients who require hormone replacement therapy, such as menopausal patients. However, in cases where there is any doubt, switching to a natural cycle is always an option. In a natural cycle, the window of implantation is always open.

Nowadays, to see when the window implantation it’s open, it’s a genetic test that tells us where the cells of the endometrium are ready and expresses the correct genes to receive the embryo and to make the implantation successful. It’s a small biopsy of the endometrium while preparing for an embryo transfer but you don’t actually do the embryo transfer – you just do the small biopsy on the endometrium and check on those genes that it tells you if the endometrium is ready to receive an embryo. When and why – it’s used a lot when you have patients with implantation failures, when you’ve been transferring good quality embryos and you don’t get pregnancies (even if they are biochemical pregnancies), so you start suspecting about the characteristic of the endometrium and the functionality of the endometrium and this is one of the tests that you can do to study.
I’m not a fan of the ERA test to tell you the truth. It was a good idea at the beginning but nowadays we know that we can control the window of implantation by using the correct hormone therapy and if I measure the progesterone in the different moments of the preparation, I can control the window of implantation. That’s why the era test it’s very pretty but actually nowadays doesn’t make a difference.

Nowadays there is a test called ERA or endometrial receptivity essay where we try to optimize the implantation window to that particular woman.

ERA test or Endometrium Receptivity Array test is a test or examination which should show us if the endometrium is receptive at the time we perform the transfer. So, of course, after an IVF failure or after a repeated failure, we bring about the ERA test examination. The examination is performed like a preparation for a frozen embryo transfer. So, estrogen-progesterone is used in encoding, the protocol, and at the time when we should perform the frozen embryo transfer, we perform the ERA test. When the cycle is finished we wait for the result. The result shows us or tells us precisely if the endometrium was at that time receptive, post-receptive, or early receptive. And the result tells us also the exact number of hours when we should perform the cycle later or earlier.

ERA test is the Endometrial Receptivity Test. So, this test is based on 238 genes, implantation genes. So, each of these genes is responsible for the production of a very important substance, which is extremely needed for embryo development in the uterus. And so, when we know the level of activity of each of these genes, we are able to determine the implantation window precisely compared with previous receptivity tests, which were based on histological examinations. So to perform the ERA test we have to make the endometrial biopsy at the time of presumed window of implantation. Afterward, we test this endometrium using NGS Next Generation Sequencing, and the conclusion of the test can be that the widow of implantation is misplaced or abnormal. In cases where it is displaced, it can be either pre-receptive, so that would mean that we have to administer progesterone longer and later transfer the embryos as usual. In a post receptive test, it will mean that we have two different embryos earlier and transfer them earlier. So based on the ERA test and scan of endometrium we can proceed with personalized embryo transfer, these are options based on freezing all embryos, and afterward, the window of Implantation is detected. And we transfer these embryos according to the detection of the window for implantation. So, it’s a very nice study published by Carlos Simone, one of the authors of the ERA test. So he showed in his five-year multi-central randomized control trial, that using personalized embryo transfer can significantly improve the implantation rate, clinical pregnancy rate, live birth rate, using personalized embryo transfer, then using just frozen embryo transfer or fresh embryo transfer.
It is also very nice in our Canadian study, which studied 20% of patients who failed to achieve pregnancy after one euploid embryo transfer, so they had a displacement of a window of implantation, that is why they use the personalized embryo transfer just after one failed IVF attempt was the transfer of the euploid embryo. So in our practice, we use a receptive test but we use our own test which is also based on the analysis of implantation genes. We have good results with it, it’s cheaper than the ERA test. So, there are some subgroups where we observe the displacement of the window of implantation more often than other patients with genital malformation, different shapes of uterus (bicornuate, AT shaped uterus). There can be some patients with endometriosis but usually we perform the endometrium receptivity test after at least transfer of two euploid embryos or after conventional transfer of high quality two blastocysts in young age groups, like up to 35 years old.

The ERA (Endometrial Receptivity Array) is a very simple test. It’s normally performed on women who had multiple unsuccessful embryo transfers. The goal of the test is to figure out the perfect moment for the implantation to take place. It’s mostly performed during stimulated cycles – on a certain day of progesterone treatment, we do an endometrial biopsy. The sample we acquire is sent for genetic testing. The results of this test tell us the perfect window of implantation. This timing window applies to all types of embryo transfer, however, the test is most commonly performed during donor egg or donor embryo treatments.

Current research based on the results of ERA tests states that around 25% of all donor egg or donor embryo patients have problems with implantation. The reasons for that can be numerous – from embryo quality to immunological causes. However, if the embryo is of good quality and the transfer does not result in a pregnancy, it’s worth considering an ERA test.

Embryo implantation is a very complex process that takes place at a very specific moment in the endometrial cycle. Not every woman has the same receptivity window, which is an important factor for the success of IVF programs. When we experience IVF failures, we have to know what the possible cause was. While the embryo is usually the main cause of failure, as its quality determines the chances of pregnancy, we can’t forget that the endometrium is a very important part of the cycle. We have to know that it’s ready at a very specific moment. If we encounter an IVF failure despite using high-quality embryos, or if we experience miscarriages or biochemical pregnancies, we need to investigate further.

The endometrial receptivity test tells us whether there’s a problem with the endometrial receptivity window, which would mean the transfer needs to be performed at a slightly different time. Some patients are receptive slightly earlier or later than we initially think they are; once we determine that’s the case, we adapt our protocols.

In order to perform an endometrial receptivity cycle, we prepare a normal cycle; instead of transferring the embryo, however, we perform an endometrial biopsy at the moment, we would normally perform the transfer. Through genetic analysis of the sample allows us to determine the exact time we need to perform the transfer.

Successful embryo implantation depends on two main factors: embryo viability and a proper endometrial environment. The short period in which the uterus is receptive to embryos is called the window of implantation. It is determined by the balance between two hormones – estrogen and progesterone. For most women, this period of receptivity occurs around six days after ovulation and lasts for four days afterwards. However, for some patients, this implantation window can be somehow displaced – as in, takes place a little earlier or later.

When treating infertile women, timing is the key. If the embryo is implanted outside this window of implantation, it could find itself in an environment not ready for it – whether, it’s pre-receptive or post-receptive, transferring embryos at the wrong time can result in implantation failure. The endometrial receptivity test (ERA) allows us to accurately determine the implantation window of each patient. It’s a genetic test that evaluates several specific genes in endometrial tissue using RNA sequencing. The endometrial biopsy must be performed on a specific day of the luteal phase. The analysis classifies the endometrium as receptive or non-receptive. Thanks to the information provided by the test, we can personalize the transfer time for each patient.

The technique seems like a sure-fire way to improve implantation chances; current research, however, doesn’t support its widespread use, as it doesn’t help every patient equally. Currently, we consider it to be most useful for patients experiencing recurrent implantation failure when we’re using high-quality embryos. Within these specific circumstances, the risk of having a displaced implantation window is significantly increased (up to 25%, according to current data).

Moreover, new genetic tests for the endometrium are becoming available, which offers additional information about the uterine environment – such as microbiological conditions or immunological status. These tests may soon enter widespread use for other patients as well.