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ERA (Endometrial



ERA, also known as Endometrial Receptivity Analysis or Array is a genetic test that evaluates a small sample of a woman’s tissue to determine the best WOI (Window Of Implantation). ERA evaluates the status of Endometrial Receptivity and also identifies a patient’s unique WOI. In short, ERA finds the best timing for transplantation to occur in the womb from a molecular point of view which is unique to each individual. The WOI which lasts a few days long during a woman’s menstrual cycle occurs when progesterone creates a perfect state of implantation. At this stage, the endometrial cells are receptive to the implant of a developing embryo. The WOI generally occurs between days 19 to 23 of a woman’s menstrual cycle, but for some women, the WOI occurs later or earlier.

How is ERA done?

ERA requires a sample of the uterine lining obtained at a specific time in the cycle. The biopsy can be done via the “Natural Cycle” or  “Mock Frozen Embryo Cycle”.


Natural Cycle:


When the follicle achieves the size of > 18mm during a woman’s cycle, hCG is administered. This usually occurs during day 14. Progesterone is given after 24 hours, on day 16 for 6 consecutive days, and a biopsy is done on day 21.


Mock Frozen Embryo Cycle:


Also known as the HRT cycle, supplemental estradiol is taken daily from the 1st day of the cycle. After 2 weeks of estrogen therapy, the endometrial lining should achieve a thickness of >6.5mm. Exogenous progesterone and estradiol can then be administered for 5 full days and the biopsy is done on the 5th day of progesterone intake.

During the biopsy, a tiny sample of the endometrial lining is acquired through a catheter through the woman’s cervix. This is a quick and painless procedure, however, some women find this uncomfortable. The sample will be sent for NGS – Next-Generation Sequencing to analyze the 248 genes to assess the optimal time to place an embryo into the uterus to promote successful implantation and pregnancy. The timing of the embryo transfer is adjusted accordingly to each individual to determine the pre-receptive, receptive, and post-receptive phases of the endometrium.


Who needs ERA?

ERA may be useful in women who experience recurrent implantation failure. The general guideline for recurrent implantation failure refers to 2 or more implantation failures during the IVF cycle with a good number of eggs at retrieval, a good fertilization rate, the embryos appear to be healthy and of high quality, the uterine lining looks good, the transfer goes smoothly, but the pregnancy never “sticks.”

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