ERA (Endometrial Receptivity Array) is a personalised genetic test to determine the receptivity of the endometrium (i.e., the test identifies when the uterine lining is ready for embryo implantation within a specific period). Using this molecular diagnostic tool, the RNA (ribonucleic acid) of an endometrial tissue sample is hybridised and then genetic expression levels of 238 genes are analysed to determine the state of receptivity of the uterine endometrium. It is determined by a computer programme using specific gene expression profiles. ERA test helps calculate the best time for embryo implantation for each woman individually.
In a study, this test was done in patients with failed implantation of a good quality embryo (at least three unsuccessful embryo transfers with in women under 37 years of age or two unsuccessful embryo transfers in women over 37 years of age). It is recommended for patients with anatomically unchanged uterus and normal endometrial thickness (≤6 mm) without apparent changes. The implantation window ‘shift’ was identified in about 20% of the patients. This test helps predict the implantation window, thus allowing scheduling a personalised embryo transfer time based on individual results.
The ERA test has shown high sensitivity and specificity in the detection of genetic expression profiles. Until now, the best embryo implantation time has been determined based on histological criteria, which are subjective and do not include any special criteria for patients with diagnosed or undiagnosed infertility. The ERA test does not have these problems, as individual data for each patient are obtained and it allows identifying the optimal endometrial receptivity time for embryo implantation.
The test requires an endometrial biopsy in the woman’s natural or hormone replacement cycle at a stage corresponding to the maximal endometrial receptivity phase. I.e., on day 21 of the natural cycle or seven days after LH (luteinising hormone) surge (LH+7, or on the sixth day after follicle rupture (ovulation) if ultrasound exam is performed), or five full days after start of progesterone in hormone replacement therapy cycles. Immediately after taking, a biopsy sample is placed into a cryotube with liquid that ensures tissue preservation and delivered to the lab at the University of Valencia (Spain). The result is available 20 days after the receipt of the sample.