Endometrial Receptivity Analysis (ERA)

ERA (Endometrial Receptivity Analysis) is a lab test on a small sample of the endometrium, the lining of the uterus. The test measures which genes are active in the sample (gene expression). Its goal is to estimate the timing of a woman's own window of implantation (WOI). The WOI is the span of days when the lining can accept an embryo. The test checks the activity of about 250 genes. The lab then labels the sample receptive, pre-receptive, or post-receptive. It also recommends a new time for embryo transfer.¹²

ERA is used with IVF frozen embryo transfer. The test assumes that some women have a shifted WOI. In these women, the standard transfer time misses the peak readiness of the lining. The theory holds that a personalized transfer time will raise live birth rates.

The randomized trial evidence does not support this theory for IVF patients in general. A randomized clinical trial in JAMA (2022) compared ERA-timed transfer with standard timing in 767 patients. Live birth occurred in 58.5% of the ERA group and 61.9% of the standard group. The difference was not statistically significant (rate ratio 0.95, 95% CI 0.79 to 1.13). ERA timing did not improve live birth.³

A later study looked back at women with repeated implantation failure. This retrospective cohort reported better outcomes.⁴ However, observational findings in a selected group cannot show that ERA works for IVF patients as a whole. The randomized trial remains the stronger evidence.

ERA does not look for the causes of implantation failure. It measures gene activity in the lining at one point in time and recommends a change in timing. It does not identify or treat the conditions that directly impair implantation: chronic endometritis, adenomyosis, fibroids that bulge into the uterine cavity (submucosal fibroids), and polyps. Identifying the root cause of implantation failure requires a different workup.⁵