The Endometrial Receptivity Array: what it tests, who it actually helps

The Endometrial Receptivity Array (ERA) tests whether your uterine lining is at the optimal day for embryo implantation by analysing gene expression in a small biopsy. It was once promoted as universally beneficial. The current evidence is more specific – and worth understanding before you pay for it.

What the ERA is checking

In a typical hormonally-prepared frozen embryo transfer cycle, the embryo is transferred after exactly 5 days of progesterone (P+5). The ERA samples your endometrium at P+5 and analyses the expression of approximately 248 genes associated with implantation. The result tells you whether your “window of implantation” is on time, displaced earlier, or displaced later.

What you do with the result

If the ERA reports a “receptive” result at P+5, transfer timing in subsequent cycles stays standard. If it reports “pre-receptive,” your embryo transfer is shifted forward (P+5.5 or P+6). If “post-receptive,” it is shifted earlier. The personalised window is then used in the actual transfer cycle.

Where it appears to help

The strongest evidence for ERA is in patients with repeated implantation failure – typically defined as failure to achieve pregnancy after three or more good-quality embryo transfers. In this subset, displaced windows of implantation are more common, and adjusting transfer timing has improved live-birth rates in observational studies.

Where the evidence is thinner

For patients on their first or second transfer, large randomised studies have not demonstrated meaningful benefit from routine ERA. Universal ERA before any transfer is not currently supported by major fertility societies and adds cost and a biopsy without clear benefit for most patients.

What the test costs you

An additional menstrual cycle of hormonal preparation (estrogen plus progesterone) without a transfer at the end. The biopsy itself, which is brief and uncomfortable but not significantly riskier than a routine endometrial biopsy. Financial cost varies by clinic and lab. And one cycle of additional waiting.

Questions worth asking your doctor

• Given our number of prior transfers and embryo grades, does the evidence support ERA for us specifically?
• If the result comes back displaced, how confidently can we transfer at the new window?
• What is your clinic’s experience with ERA-adjusted transfers – what does the success rate look like compared to standard timing?
• Is there an alternative (a “mock cycle” with serial progesterone monitoring) that gives similar information at lower cost?

This essay is educational. Every patient’s situation is different – the right plan is shaped in conversation with a fertility specialist who knows the full picture.