Chronic endometritis: link with implantation failure

What is chronic endometritis?

The endometrium is the lining of the inside of the uterus, which receives the embryo. Chronic endometritis is a low-grade inflammation of this lining that persists over time.

It is clearly distinct from acute endometritis, an overt infection that occurs for example after childbirth, a miscarriage or an intrauterine procedure, and which causes fever, pain and abnormal discharge. Chronic endometritis, on the other hand, is most often silent: it causes neither fever nor pain and is only discovered during tests carried out as part of an infertility assessment.

Its origin is thought to be mainly bacterial, with a variety of germs (intestinal germs, streptococci, mycoplasmas, etc.), but the mechanisms remain incompletely understood. Hypotheses involving the gut or vaginal microbiota are being studied, with no practical application to date.

What is the link with implantation failure?

Recurrent implantation failure refers to the situation where several transfers of good-quality embryos do not result in pregnancy. The causes are multiple: embryo quality (often linked to age), abnormalities of the uterine cavity, immunological or unknown factors.

Chronic endometritis has been proposed as one of the possible causes, because inflammation of the endometrium could disrupt the reception of the embryo. The available data show an association, not a demonstrated cause-and-effect relationship:

Source: meta-analysis of 39 studies (Mihoci et al., 2026). GRADE level of evidence low to very low for all outcomes.

These figures mean that the difference exists on average, but that a majority of women with chronic endometritis still achieve a pregnancy. They do not make it possible to state that endometritis is responsible for the failures observed in a given woman.

How is the diagnosis made?

There is currently no universal definition of chronic endometritis, which partly explains the differences between studies.

The 2026 meta-analysis concludes that hysteroscopy should be considered a complement to biopsy, and not a diagnostic test on its own.

In practice, the biopsy is performed at the practice, using a thin cannula inserted into the uterus, without anaesthesia, in a few minutes; the timing in the cycle is explained to you at the consultation. The result depends on the experience of the pathology laboratory and the technique used.

Who should be tested?

The authors of the most recent meta-analysis consider that systematic screening before a first IVF cannot be recommended in view of current data. Targeted testing can be discussed in selected women; the good practice recommendations of ESHRE (the European Society of Human Reproduction and Embryology, 2023) state that it can be considered after recurrent implantation failure, with antibiotic treatment if the diagnosis is confirmed:

• recurrent implantation failure after transfer of good-quality embryos;
• recurrent miscarriage with no cause found;
• unexplained infertility after a complete assessment;
• suggestive appearance discovered during a hysteroscopy performed for another reason.

This testing is part of a broader assessment, which includes in particular evaluation of the uterine cavity (polyps, adhesions, septum, fibroids) and of ovarian reserve.

How is chronic endometritis treated?

Treatment is based on oral antibiotic therapy, with drugs active against a broad range of germs; the regimen (drugs and duration) is explained to you at the consultation. Protocols vary from one study to another and none has been validated by a large trial.

A follow-up biopsy is often offered after treatment to check that the inflammation has disappeared. If it persists, a second course of treatment may be discussed.

Does treatment improve the chances of pregnancy?

This is the central question, and the answer remains uncertain.

A meta-analysis published in Fertility and Sterility in 2018, involving women with recurrent implantation failure, showed that:

• women simply treated with antibiotics, without checking for cure, did not have better results than untreated women;
• women whose cure was confirmed by a follow-up biopsy had clearly higher ongoing pregnancy or live birth rates than those whose endometritis persisted;
• cured women achieved results comparable to those of women without endometritis.

The 2026 meta-analysis reaches the same conclusion: women whose endometritis has resolved have better results than those in whom it persists.

These results are encouraging but must be interpreted with caution:

• they come almost exclusively from observational studies, not randomised trials;
• women in whom the inflammation disappears could differ from others for other reasons;
• definitions, plasma cell thresholds and the antibiotics used vary widely from one study to another.

In summary, it has not been demonstrated that screening for and treating chronic endometritis increases the number of births. Randomised trials are awaited.

What are the drawbacks of unnecessary treatment?

Prescribing antibiotics is not without consequences:

• digestive side effects, vaginal thrush, allergic reactions;
• contribution to bacterial resistance to antibiotics;
• risk of delaying the search for other causes of failure, which are sometimes more decisive.

This is why the approach favours targeted testing, a histological diagnosis and clear information about the uncertainty.

Frequently asked questions

General information article: it does not replace a medical consultation. In an emergency, call 15 or 112 in France, or your local emergency number.