An endometrial receptivity array (ERA) is a type of test used on women going through IVF to determine the optimal timing for embryo implantation. It is primarily used for cases of repeated implantation failure following embryo transfer.
After sperm fertilizes an egg to form an embryo, that embryo moves from the fallopian tubes to the uterus where it implants into the endometrium, or uterine lining.
If IVF is used, then the embryo is formed in the lab rather than in the fallopian tubes. Implantation will happen after embryo transfer, when the embryo is put directly into the uterus.
To prepare for pregnancy, the endometrial lining in the uterus thickens and becomes receptive to implantation of a fertilized egg. This happens in response to hormone secretion, with estrogen and progesterone being the primary hormones that are released to ensure the endometrial lining is receptive to pregnancy. The external cells of the embryo and the uterine inner lining, together, will create the future placenta.