Endometrial Receptivity Array (ERA Test)
Definition - What does Endometrial Receptivity Array (ERA Test) mean?
An endometrial receptivity array (ERA) is a diagnostic tool that helps evaluate the receptivity of the innermost lining of the uterus called endometrium in women with repeated in vitro fertilization (IVF) or implantation failure.
Endometrial receptivity (ER) is a state during which the endometrium is optimally receptive to implanting (accepting) an embryo. The ERA evaluates the quantity of RNA (ribonucleic acid) produced by the cells of the endometrium and determines the stage at which the endometrial lining is optimally developed to accept an embryo. It, thus, boosts the odds of a successful embryo transfer.
Endometrial receptivity array is also known as an ERA test.
FertilitySmarts explains Endometrial Receptivity Array (ERA Test)
For a successful IVF cycle, an embryo needs to be transferred at an appropriate stage of a woman’s cycle. This stage usually occurs between days 19 to 21 of the menstrual cycle (i.e. 5-7 after ovulation). This period of receptivity is referred to as the “window of implantation.” Transferring an embryo at a wrong stage in its development causes implantation failure. Repeated implantation failure is a failure of at least three IVF cycles which involved the transfer of one or two high-grade embryos.
The ERA analyzes the expression levels of 238 genes involved in endometrial receptivity. An endometrial biopsy is first performed either during a natural cycle or a hormone replacement therapy (HRT) cycle to obtain a sample of the endometrial tissue. During a natural cycle, a woman uses an ovulation predictor kit to detect the LH (luteinizing hormone) surge. This is labeled as day 0. The woman then visits her fertility doctor on day 7 for the endometrial biopsy and the ERA test. If HRT is used to prepare the uterine lining, the day the progesterone is started is marked as day 0. The ERA test is then done on the fifth day.
The biopsy sample is then sent to the laboratory where the expression of endometrial receptivity genes is analyzed. Computers are used to analyze the amount of RNA produced during several times of the cycle. RNA is a nucleic acid that allows the transfer of genetic information from DNA (deoxyribonucleic acid) to proteins. This helps determine a personalized window of implantation for each woman. An ERA predictor analyzes the data and classifies the endometrium as either “receptive” or “non-receptive.”
A receptive endometrium implies that a woman’s window of implantation was on the day of the cycle when she underwent the biopsy, therefore, allowing the embryo transfer into the uterus during this period.
A non-receptive endometrium has a displaced window of implantation. In this case, the procedure will be repeated based on the data collected from the computational ERA predictor. This will give a new estimation of a woman’s personalized window of implantation, with the goal of increasing the odds successful implantation of an embryo in the next cycle—a process called personalized Embryo Transfer (pET).