- By: Jananam
- March 17, 2025
Endometrial Receptivity Assay (ERA) – Process
An endometrial receptivity assay (ERA) tests whether the uterine lining is ready to accept an embryo. The endometrium is receptive for only a short window each cycle, and ERA identifies when that window falls for you, so embryo transfer can be timed to it rather than to a standard calendar day.
The endometrium has to be receptive enough to let implantation occur. ERA is a test that allows us to know if the implantation will occur or not.
Endometrial receptivity is essential for successful implantation.
Endometrium
Endometrium is a tissue lining the interior of the uterus where the embryo attaches and grows during pregnancy.
Naturally, each month, the Endometrium gets thickened and if pregnancy doesn’t occur in that cycle, periods begin then.
Em Receptivity
Receptive Endometrium means that the uterine lining is ready for the implantation of the embryo.
The period of receptivity is usually between days 19-21 of the menstrual cycle. This is called the window of implantation.
Displaced window of implantation
The phase of receptive Endometrium will not be the same in all women. Their optimal day for embryo transfer could be different from the defined window of implantation. (19 – 21 days of menstrual cycle)
3 in every 10 patients have a displaced window of implantation.
Preparation for ERA
On day 2 of your periods, a scan will be done to ensure that your uterine lining is thin and you will be given estrogen tablets for about 7 – 12 days and once the endometrial thickness is adequate, progesterone levels in your blood will be tested.
You will be started on progesterone injections after evaluating your blood test and on the 6th day of your injection, ERA test will be done.
Procedure
Using a fine pipette catheter, a sample of the uterine lining will be taken in the OP room. The same will be sent for evaluation.
Results
The ETA test establishes the best day for transferring the embryo. About 248 genes that are involved in determining receptivity are analysed.
Benefits
It will allow for a personalized embryo transfer. The chances of getting pregnant are increased after personalized embryo transfer.
The ERA test resulted in a 73% pregnancy rate in patients with implantation failure. Your embryo transfer will be timed according to the report.
After ERA, you will be given some tablets for about 2 weeks and the embryo transfer will be planned in your subsequent cycle. Once we receive the report, you will be informed of the same by one of our hospital staff.
What is an endometrial receptivity assay?
What does an ERA test actually measure?
It measures whether the endometrium, the lining of the uterus, is receptive to an embryo on a given day. Receptivity normally falls between days 19 and 21 of the cycle, a period called the window of implantation, and the assay checks whether yours matches that.
Who needs an endometrial receptivity assay?
It is most useful where good-quality embryos have failed to implant without an obvious explanation. Around 3 in every 10 patients have a displaced window of implantation, meaning their optimal transfer day differs from the standard one.
How is the ERA cycle prepared?
On day 2 of your period a scan confirms the lining is thin. Estrogen tablets are then given for about seven days, followed by progesterone, mimicking a frozen transfer cycle. A small biopsy of the endometrium is taken at the point where transfer would normally happen.
What happens after the ERA result?
If the lining is receptive on the day tested, transfer is timed as usual. If the window is displaced, the transfer day is shifted by the interval the result indicates, so the embryo is placed when your endometrium is genuinely ready.
Is the ERA biopsy painful?
Most women describe brief cramping similar to period pain rather than sharp pain. It is done in the clinic without general anaesthesia, and normal activity can usually be resumed the same day.
How much does an ERA add to a treatment cycle?
It requires a preparatory cycle of its own, because the biopsy is taken at the point where a transfer would otherwise happen. That means the transfer is deferred to a subsequent cycle. This is why it is reserved for situations where good embryos have repeatedly failed to implant rather than used routinely.
An endometrial receptivity assay is one part of a wider picture. Where transfers have repeatedly failed, the assessment usually also revisits the IVF cycle itself and whether hysteroscopy is warranted to look directly at the uterine cavity.
Related reading
Clinical references
Independent clinical guidance relevant to this topic:
