Chronic endometritis was found in 41.7% of women with diffuse adenomyosis of the inner myometrium and 13.7% of women without that pattern. A Spanish study examined how the two uterine conditions might overlap in patients evaluated for infertility, recurrent miscarriage or repeated implantation failure.
When several IVF transfers have failed, or pregnancy is followed by repeated miscarriage, an embryo assessment and hormone tests may leave questions unanswered. One possible area to investigate is the uterus itself. In a study of 332 women undergoing fertility evaluation, chronic inflammation of the uterine lining was more frequent in women with a particular form of adenomyosis.
How do the conditions differ?
In adenomyosis, tissue resembling the uterine lining occurs within the muscular wall. It can cause painful or heavy periods and pelvic pain, and may affect pregnancy and birth in some women. Adenomyosis can be focal or spread diffusely through the muscle. Changes at the boundary between the lining and muscle may affect uterine structure and function.
Chronic endometritis is persistent inflammation of the uterine lining itself. Unlike acute inflammation, it often causes few obvious symptoms. Diagnosis generally involves identifying plasma cells in an endometrial biopsy, sometimes using CD138 immunohistochemical staining. The disorders affect different tissues but both may be relevant to the environment for implantation and pregnancy.
Chronic endometritis in 41.7% of women with the diffuse inner-layer pattern
Among the 332 patients, chronic endometritis was approximately three times as prevalent in those with diffuse adenomyosis of the inner myometrium as in those without that pattern (41.7% versus 13.7%). The association persisted after adjustment for factors including age and uterine fibroids. The adjusted odds ratio was 4.33. That figure describes the odds of the conditions coexisting and cannot be read as a precisely 4.33-fold increase in the risk of developing the disease.
Why the uterine environment matters in repeated implantation failure
IVF outcomes depend partly on the endometrium in which an embryo implants. Even a good-quality embryo may encounter difficulties if the lining or uterine environment is impaired. Adenomyosis has been linked to questions about contractions, inflammation and changes at the junction of lining and muscle. Researchers are also studying how chronic endometritis might affect the immune environment and implantation.
This study shows that the conditions can coexist in some patients. It did not establish that adenomyosis causes chronic endometritis, quantify a change in implantation or miscarriage when both are present, or demonstrate that treating inflammation improves birth rates. The finding offers a reason to consider both conditions in an evaluation without assigning recurrent implantation failure or miscarriage to a single cause.
Should everyone with adenomyosis be tested?
The participants had been referred for infertility, recurrent miscarriage or repeated implantation failure. The prevalence figures should not be applied to all women with adenomyosis. The study cannot support testing every patient. Diagnostic criteria, test methods and the effects of treatment on pregnancy and birth all need further study.
For a patient with adenomyosis and repeated losses or implantation failure, a clinician may consider these findings alongside symptoms, prior investigations and the state of the endometrium when discussing whether evaluation would help. A single result rarely explains a failed pregnancy. Both embryo quality and the structure and inflammatory state of the uterus may merit attention, with decisions tailored to the individual clinical situation.
Source: “Association between adenomyosis of the inner myometrial layer and chronic endometritis: a retrospective cohort study.” Reproductive BioMedicine Online, published online July 29, 2026, November issue, article 105895. DOI: 10.1016/j.rbmo.2026.105895. PMID: 42659759. The illustration depicts a fictional scene.
Related reading: Adenomyosis pattern and live birth: a review of 19,510 women.
Copyright © 2026 Fertility Information TokTok Fertility News | THE FERTILITY NOTES. All rights reserved. Unauthorized republication, reproduction, redistribution, scraping, AI training and data use of any content, including articles, photographs and images, are strictly prohibited. Violations may result in legal liability.