ERA test

Endometrium Receptivity Array test used to determine the exact ideal time for replacement of embryos to the womb.

An Endometrial Receptivity Array (ERA) test is performed before frozen embryo transfer in certain patients. The test aims to determine whether or not the endometrial cavity is ready for implantation so that a fertility specialist knows the best time for the embryo transfer to take place.


Carrying out this testing will allow a specialist to identify the specific time for embryo implantation for each individual patient. For most patients, their uterus will be most receptive to receiving an embryo at around Day 19 to Day 21 of their menstrual cycle. This will be when most embryo transfers are performed. However, for some women, or for non-binary or transgender patients looking to conceive, the ideal window of implantation may be earlier or later than this. Some experts have even suggested that this might be one of the reasons behind failed cycles of IVF.

An ERA test will allow fertility specialists to assess whether or not their patient’s uterus is ready for implantation at the expected time. Based on the results received, they will then be able to alter the time or date of the embryo transfer in the hopes of improving the chances of success. 

There are three stages to an ERA test. The first of these is the endometrial biopsy. In this time, the patient will be instructed to take hormones similar to those in a frozen embryo transfer cycle. This will be timed to when the specialist believes the patient’s uterus should be most receptive and will be carried out using a pipelle. This allows the doctor to “scratch” the uterine lining to obtain a small amount of tissue for testing. It is an outpatient procedure and should cause minimal discomfort.

The endometrial tissue collected will then be taken for the second stage of the test. This involves transferring it to a tube containing fluid, preserving it for the duration of its journey to a genetics laboratory. Once there, the final stage of the test ‒ molecular analysis ‒ will be carried out to determine the best time to carry out an embryo transfer.

Three possible results can come back from having this test carried out:

  • The patient’s lining is pre-receptive, meaning it is not yet ready to receive an embryo
  • The patient’s lining is receptive, meaning it is ready to receive an embryo
  • The patient’s lining is post-receptive, meaning that the window for implantation has been missed for this cycle

It should be noted that research around ERA tests have not found concrete proof to suggest that they increase the chances of IVF success. Currently, ERA is outlined as a treatment add-on by the Human Fertilisation and Embryology Authority (HFEA). It is also listed as red in the HFEA traffic light system, owing to the fact that there is no evidence from randomised controlled trials (RCTs) that it improves the chances of having a baby for most fertility patients.