Thin endometrium: when the lining, not the embryo, is the obstacle

The lining of the womb, or endometrium, thickens under the influence of oestrogen during the cycle or during preparation for an embryo transfer. It is measured by ultrasound, and a thickness of around 7 millimetres or more, with a layered appearance, is usually considered sufficient to receive an embryo. This is not an absolute cut-off; some pregnancies occur with a slightly thinner lining, and a single number is never taken in isolation.

What matters is the whole picture: the thickness, the pattern of the lining on ultrasound, and the clinical context. A single measurement a little below expectation therefore does not necessarily mean transfer must be stopped; it is a signal to look at the situation carefully.

A thin endometrium can have several causes. The most common is previous damage to the basal layer of the lining, for example after a curettage, after an infection, or after adhesions inside the womb called Asherman's syndrome. In other cases the cause is limited blood flow to the lining, or a weak response to oestrogen. Sometimes no clear cause is found.

Identifying the cause changes the approach. If there are adhesions inside the womb, they can be treated with hysteroscopy before improvement of the lining is expected. If the lining simply responds slowly to hormones, the solution may be more time or an adjustment to the hormonal support. The first step is therefore to understand why the lining stays thin, not simply to measure it again.

Management depends on the cause. Where there are adhesions, hysteroscopy to remove them is the main step. Where the lining responds slowly to oestrogen, increasing or extending oestrogen support, changing the route of administration, or simply more time within a cycle can help. For many women, simply waiting and repeating the preparation in another cycle allows the lining to reach the right thickness.

There are also additional approaches still being studied and used in selected cases when standard methods are not enough. These are discussed individually, because the evidence for them is more limited. The main message is that a thin endometrium is rarely a dead end; it calls for patience and a considered plan, not a rushed transfer.

Because embryos can be frozen and stored, there is no need to transfer a good embryo into a lining that is not ready. Postponing the transfer to another cycle, while the embryo stays safely frozen, is often the wiser decision. This gives the team time to improve the lining and gives you the best chance at transfer.

Waiting can be emotionally hard, especially when you have already waited a long time. But a single good transfer, in the right conditions, is worth more than several rushed transfers into an unprepared lining. The team explains this from the start, so that the decision to wait feels like a choice, not a failure.