What is endometrial receptivity (ERA), and why does timing matter?

In IVF, a great deal of attention goes to the embryo — and rightly so. But an embryo can only implant if it is transferred when the uterus is ready to receive it. That short, specific stretch of time is called the window of implantation, and understanding it is what endometrial receptivity is all about.

The window of implantation

The lining of the uterus (the endometrium) changes across the menstrual cycle. For a few days, it becomes receptive — biologically prepared for an embryo to attach and implant. Transfer too early or too late, and even a high-quality embryo may fail to implant.

For most patients this window is well-timed, but for some it is displaced — shifted earlier or later than the standard protocol assumes. Repeated implantation failure despite good embryos is often a sign that timing, not embryo quality, is the missing piece.

How receptivity is assessed today

Endometrial Receptivity Analysis (ERA) traditionally involves an endometrial biopsy — a small tissue sample analysed for the expression of receptivity-related genes to pinpoint the personal window. It works, but it is:

• Invasive — it requires a biopsy procedure.
• Costly and time-consuming — often adding a dedicated cycle.
• A barrier — enough that many patients who could benefit never have it done.

A less invasive direction

Garbha ERA is being built to estimate endometrial receptivity from standard ultrasound imagery using AI — a non-invasive alternative to surgical biopsy. The goal is to make personalised transfer timing:

• Accessible — using imaging clinics already perform.
• Lower-risk and lower-cost — reducing reliance on biopsy.
• Actionable — helping clinicians choose the optimal transfer day for each patient.

Garbha ERA is currently in build; EmbryoScore is the module in clinical use today.

Why it matters for outcomes

Personalising the transfer window means fewer cancelled or failed transfers for patients whose window is displaced — and less emotional and financial strain from repeating cycles. Precision on timing complements precision on embryo selection: together they give each transfer the best possible chance.

Further reading

• World Health Organization — Infertility
• ESHRE — Guidelines & resources
• ASRM — Patient resources

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