Stop guessing your transfer day.

The endometrium is only receptive to an embryo for a short span of time each cycle, commonly called the window of implantation. Standard practice assumes that window falls at the same point for everyone and schedules the transfer accordingly. For most women that assumption holds. For a minority it does not, and their window is shifted earlier or later by a day or more — which means a perfectly good embryo can be transferred into a uterus that simply is not ready for it.

Endometrial Receptivity Analysis is designed to find those cases. A small sample of endometrial tissue is taken in a mock cycle that exactly mimics the hormonal preparation of a real frozen embryo transfer. The sample is analysed for the expression pattern of a large panel of genes involved in implantation, and the result reports whether the endometrium was receptive at the moment of biopsy, or whether it was pre-receptive or post-receptive.

If the window is shifted, the fix is precise rather than dramatic: the next transfer is moved forward or back by the number of hours the test indicates. This is called a personalised embryo transfer, and it converts an educated guess about timing into a measured one.

The biopsy itself is a brief outpatient procedure needing no anaesthesia, comparable to an IUD insertion, with cramping for a short period afterwards. Because the sample must be taken in a mock cycle, it does add one cycle before the transfer that follows.

This test is not part of routine IVF, and should not be. It is aimed at a specific group: women with repeated implantation failure — good-quality embryos transferred into a normal-looking cavity that have nonetheless not implanted — once the more common explanations have been excluded. Offering it to everyone adds cost and delay without benefit, and it is worth being told plainly whether your history actually fits the indication.