When you’ve been trying to get pregnant for some time and are considering invitro fertilization (IVF), you want everything to go right. Unfortunately, IVF does not work every time and your doctor many not always be able to determine the reason why your IVF failed. As part of the IVF failure workup, many doctors use the endometrial receptivity array (ERA), to evaluate issues with the receptivity of the uterus that may have caused implantation failure. However, this is only indicated in specific situations. So, when should you do the ERA test? Let’s learn:

What is the Endometrium?

The endometrium is the inner lining of the uterus, which thickens and sheds during your menstrual cycle. During an IVF cycle, the doctor will give you medications to prepare and thicken the endometrium to prepare it for receiving an embryo.  

If there is no fertilized embryo or if the one introduced during an IVF cycle does not implant, the tissue lining starts to shed, which is what you call menstruation.

Ultrasound for endometrial examination

Traditionally, the doctors have been checking the thickness of endometrial lining with ultrasounds, but with the development of the ERA test, we can now get a much better insight into the quality of the endometrium and the overall environment of your uterus. This can be crucial to embryo implantation and IVF success.

What is implantation and why does it fail?

For a pregnancy to succeed, the embryo must attach itself to the uterine wall and grow from there.

When a woman is unable to succeed with IVF despite having seemingly good embryos, it could be caused by implantation failure. If you have recurrent implantation failure (more than 2 times), the doctor will advise advanced blood tests for hormonal issues, clotting problems, and genetic diseases.

However, a conducive uterine environment is also essential for pregnancy success and you can check the receptivity of the uterine lining with an ERA test.

What is the ERA Test?

ERA is a genetic test performed on a small sample of a woman’s endometrial lining to determine the best time for embryo transfer in an IVF cycle that will give the highest chances of a successful implantation.

Your genes determine the receptivity of your endometrium as exhibited by the endometrial cells, which produce varying levels of certain kinds of RNA during the more receptive time. ERA evaluates the expression levels of the 236 genes.

After studying more than 12,000 samples of endometrial tissue, the researchers observed the levels of RNA produced during different times of the menstrual cycle. Advanced computer algorithms were then used to find reliable patterns in RNA production, which helped them label the samples as ‘receptive’ or non-receptive.’

They also found that the results of the ERA test were highly reproducible—if they retested the endometrial samples taken during a particular time in the cycle even after months, the results remained unchanged.

By examining the expression of these genes, the ERA finds a woman’s personal window of implantation (which is normally between day 19 and 23 of the period cycle), when the endometrium is most receptive. With ERA, the main goal is to determine the ideal day for embryo implantation to have the highest chances of success.

How is the ERA test performed?

The first step is the biopsy of the uterine lining, which can be simply done in-office, without anesthesia.

It is then analyzed for the genes to predict if the endometrium is ‘receptive’ or ‘non-receptive’ on the supposed day of embryo transfer. It is typically done during the ‘mock cycle’ on the day on which embryo transfer would have been done in the actual cycle.

When should you do the ERA test

A plunger attached to a thing catheter is inserted in the uterine cavity through the cervix, and it uses suction to draw a very small sample of the endometrial tissue. This is usually done very quickly but some women feel uncomfortable in the process.

This sample is then sent to the genetic lab for examination and the results of ERA test are available in approximately 3 weeks’ time.

If the endometrium is found to be adequately ‘receptive,’ the embryo transfer can be done in the next cycle using the same timing.

The hormone Progesterone is responsible for development of endometrium and it is administered for a few days before during an IVF cycle to grow the lining ahead of embryo transfer.

If the ERA test finds the endometrium to be non-receptive, your window of implantation may be displaced and the doctor will adjust the Progesterone administration accordingly to create optimal implantation environment.

Once again, the ERA test will be performed to identify the new window of implantation and if correct, the embryo transfer can be done accordingly in the next cycle.

When should you do the ERA test?

For around 80% of women, the window of implantation falls in the standard expected time. This means that 20% or 1 out of 5 women will need a different protocol to determine their unique window of implantation.

The ERA test is useful in finding the optimal time of embryo transfer in women whose window of implantation is altered so that the doctor can adjust the medications accordingly and create their personalized embryo transfer (pET) time, thus giving them the highest chances of a successful pregnancy.

You should consider the ERA test if you have:

  • Had unsuccessful implantation, despite having adequate embryo quality
  • Had more than two unsuccessful embryo transfers
  • Concerns regarding your endometrial lining

Based on your endometrial diagnosis, your fertility specialist may recommend the ERA test during your IVF cycle.

A study published in the Journal of Human Reproductive Sciences, found that using by undergoing an ERA biopsy 127 out of 175 women (72.6%) were able to have a successful pregnancy with personalized embryo transfer (pET).

So, should you do the ERA test? Although not recommended in all cases, ERA has been a key intervention for some patients, who were otherwise feeling hopeless due to recurrent IVF failures. Knowing your pET can be useful and empowering as you participate in being an informed patient during your fertility treatments.

If you feel that you might need an ERA test, discuss with your doctor and take advantage of the available technologies in this evolving science of infertility management.

Get in touch via the form on the right for more information or ask an expert for the suitability of ERA test in your situation.


Patel, J. A., Patel, A. J., Banker, J. M., Shah, S. I., & Banker, M. R. (2019). Personalized Embryo Transfer Helps in Improving In vitro Fertilization/ICSI Outcomes in Patients with Recurrent Implantation Failure. Journal of human reproductive sciences12(1), 59–66. https://doi.org/10.4103/jhrs.JHRS_74_18

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