Study results
The cohort study that matched 133 ERA patients with 353 non-ERA patients showed live birth rates of 49.62% for the ERA group and 54.96% for the non-ERA group (odds ratio [OR], 0.8074; 95% confidence interval [CI], 0.5424–1.2018).2 Of note, no difference occurred between subgroups based on the prior number of FETs or the receptivity status (TABLE 1).
Another cohort study from the University of California, Los Angeles, published in 2021 analyzed 228 single euploid FET cycles.3 This study did not show any benefit for routine ERA testing, with a live birth rate of 56.6% in the non-ERA group and 56.5% in the ERA group.
Still, the most convincing evidence for the lack of benefit from routine ERA was noted from the results of the randomized clinical trial.4 A total of 767 patients were randomly allocated, 381 to the ERA group and 386 to the control group. There was no difference in ongoing pregnancy rates between the 2 groups. Perhaps more important, even after limiting the analysis to individuals with a nonreceptive ERA result, there was no difference in ongoing pregnancy rates between the 2 groups: 62.5% in the control group (default timing of transfer) and 55.5% in the study group (transfer timing adjusted based on ERA) (rate ratio [RR], 0.9; 95% CI, 0.70–1.14).
ERA usefulness is unsupported in general infertility population
The studies discussed collectively suggest with a high degree of certainty that there is no indication for routine ERA testing in the general infertility population prior to frozen embryo transfers.
Although these studies all were conducted in the general infertility population and did not specifically evaluate the performance of ERA in women with recurrent pregnancy loss or recurrent implantation failure, it is important to acknowledge that if ERA were truly able to define the window of receptivity, one would expect a lower implantation rate if the embryos were transferred outside of the window suggested by the ERA. This was not the case in these studies, as they all showed equivalent pregnancy rates in the control (nonadjusted) groups even when ERA suggested a nonreceptive status.
This observation seriously questions the validity of ERA regarding its ability to temporally define the window of receptivity. On the other hand, as stated earlier, there is still a possibility for ERA to be beneficial for a small subgroup of patients whose window of receptivity may not be as wide as expected in the general population. The challenging question would be how best to identify the particular group with a narrow, or displaced, window of receptivity.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
The optimal timing for implantation of a normal embryo requires a receptive endometrium. The endometrial biopsy was used widely for many years before research showed it was not clinically useful. More recently, the endometrial receptivity array has been suggested to help time the frozen embryo transfer. Unfortunately, recent studies have shown that this test is not clinically useful for the general infertility population.
The optimal timing for implantation of a normal embryo requires a receptive endometrium. The endometrial biopsy was used widely for many years before research showed it was not clinically useful. More recently, the endometrial receptivity array has been suggested to help time the frozen embryo transfer. Unfortunately, recent studies have shown that this test is not clinically useful for the general infertility population.
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