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What is the Endometrial Receptivity Array (ERA) Test?

Pregnancy develops in an organ called the uterus. The lining covering the inside of the uterus is a tissue called the endometrium which prepares itself every month for the possible arrival and implantation of an embryo. When this does not happen and no embryo is present for implantation, the uterus sheds its endometrial lining and menstruation begins. One especially important factor in pregnancy is endometrial receptivity. An endometrium is regarded as receptive if it is prepared for embryo implantation to take place, which normally happens between the 19th and 21st day of a woman’s menstrual cycle (about 5-7 days after ovulation). This period of receptivity is what we call the “implantation window.”

The ERA is a test which allows us to evaluate endometrial receptivity, or a lack thereof, by means of analysing the gene expression of a group of genes related to endometrial receptivity. The test involves performing a biopsy of the endometrial tissue on day 21 of the woman’s menstrual cycle (during her receptive phase). The expression of 238 genes related to endometrial receptivity is analysed, and the endometrium is later classified as receptive or non-receptive according to a computational predictor:

  • Receptive: this means that the implantation window was open on the day that the biopsy was performed, and that they embryo will be able to implant into the uterus.
  • Non-receptive: this means that the female’s implantation window was off or was not open when it was expected to be.

In the latter case, the procedure will be repeated in accordance with the computational predictor which will give an estimate as to when the woman’s personal implantation window should be open in order to perform the embryo transfer.