Chronic Endometritis: The Missed Diagnosis Behind Recurrent Loss and Failed IVF

What Is Chronic Endometritis?

Chronic endometritis (CE) is a persistent, low-grade inflammatory condition of the endometrium, the lining of the uterus. It is not the same as endometriosis. It is not a post-surgical infection. It is a subclinical, ongoing inflammation of the uterine lining itself, driven by abnormal bacterial colonization, and in most women it produces no dramatic symptoms. That silence is the clinical trap.

In CE, plasma cells infiltrate the endometrial stroma, where they are not normally found. The endometrium is cyclically shed and renewed, which creates a false expectation that the uterine environment resets cleanly each cycle. In women with CE, it does not. The inflammatory state persists across cycles, disrupting the molecular environment required for embryo implantation and early pregnancy maintenance.

The pathophysiology involves disruption of endometrial receptivity. The normal implantation window depends on a precisely coordinated cascade of cytokines, adhesion molecules, and stromal architecture. Persistent inflammation alters this environment at the molecular level, per Kitaya et al. 2015. The embryo arrives into a hostile rather than receptive uterine milieu. This is why CE can cause implantation failure and early pregnancy loss even when the embryo appears morphologically normal and the hormonal support appears adequate.

The causative organisms are typically common bacteria: Enterobacteriaceae, Enterococcus, Streptococcus, Staphylococcus, Mycoplasma, and Ureaplasma are the most frequently identified. These are not organisms that cause obvious acute infection in most patients. They produce a chronic, low-grade state rather than acute illness, per Moreno et al. 2018. A woman can carry CE for months or years without any symptom that would prompt investigation.

CE should not be confused with acute endometritis, which is a different clinical entity discussed briefly at the end of this guide. Acute endometritis is a well-recognized, symptomatic infection typically occurring after delivery, miscarriage, or uterine instrumentation. Chronic endometritis is the quiet version. It is the one that gets missed.

Why CE Is the Missed Diagnosis

Here is the diagnostic chain that fails most patients.

A woman has two, three, or four miscarriages. Or she has three IVF cycles with good embryos that do not implant. The workup covers: karyotyping, thrombophilia panel, thyroid function, uterine anatomy assessment with a saline-infusion sonogram or hysteroscopy for structural lesions. She may receive a clotting disorder workup. She may receive immune panels. She is told the results are either normal or non-explanatory. The label assigned is "unexplained recurrent pregnancy loss" or "unexplained recurrent implantation failure."

What the standard workup typically does not include: an endometrial biopsy with CD138 immunohistochemistry to evaluate for plasma cell infiltration. That biopsy is the only test that can confirm or exclude CE. If the biopsy is not done, CE cannot be diagnosed. Not because it is not present. Because no one looked.

This is not a fringe observation. A 2022 survey of obstetricians and gynecologists found a concerning spectrum of deficiencies in awareness of CE's clinical implications, diagnostic criteria, and treatment strategies among practicing clinicians, per Margulies et al. 2022. The condition is not taught robustly. The biopsy is not reflexively ordered. And women carry the cost of that gap in the form of repeated losses and failed cycles.

In women with recurrent pregnancy loss, prevalence estimates for CE range from 9% to nearly 58% depending on the cohort and the diagnostic method used, per McQueen et al. 2014 and Cicinelli et al. 2013. The wide range reflects variation in biopsy technique, the threshold for plasma cell identification, and whether hysteroscopy or histology or both were used. But the lower bound of that range still represents a meaningful proportion of a population already defined by reproductive failure. In the implantation failure literature, CE prevalence in repeated implantation failure cohorts ranges substantially higher: Cicinelli et al. 2015 found CE in 66.0% on hysteroscopy and 57.5% on histology in a cohort of 106 women with repeated unexplained implantation failure at IVF, per Cicinelli et al. 2015.

A woman who has had multiple failed embryo transfers or multiple losses without a clear cause has a clinically meaningful pre-test probability of CE. Without the biopsy, that probability never becomes a diagnosis.

"Unexplained" recurrent pregnancy loss and "unexplained" implantation failure are not diagnoses. They are labels assigned when the workup did not look for everything. CE is one of the things the workup often does not look for.

How Chronic Endometritis Is Diagnosed

CD138 immunohistochemistry (IHC) on endometrial biopsy is the current diagnostic standard. CD138 is a surface marker expressed by plasma cells. In normal endometrium, plasma cells are not present in the stroma. When CD138-positive plasma cells are identified on IHC staining of an endometrial biopsy specimen, that is the histologic confirmation of CE, per Puente et al. 2019. The threshold for a positive result varies by study and by laboratory protocol, which contributes to the heterogeneity in prevalence estimates across the literature. This is a live methodological debate in the field.

The biopsy is a minimally invasive office procedure: a small catheter is passed through the cervix and a sample of the endometrial lining is collected. It is typically done in the proliferative phase of the cycle, outside the implantation window. The specimen is sent to pathology for standard hematoxylin and eosin staining and, ideally, CD138 IHC.

Hysteroscopy can raise clinical suspicion for CE. Characteristic findings include a "strawberry pattern" of focal hyperemia with small polypoid projections, micropolyps (small polypoid structures less than 1 mm), and stromal edema, per Park et al. 2017. These hysteroscopic findings are suggestive but not confirmatory. A hysteroscopy without a biopsy does not diagnose CE. The two investigations are complementary. Hysteroscopy can also identify co-occurring structural pathology such as endometrial polyps, which are independently associated with CE, per Vitagliano et al. 2021.

Microbial culture of endometrial samples can identify the causative organism and guide antibiotic selection. Not all causative organisms are easily culturable, however, and culture alone is insufficient for diagnosis because CE can be present without a clearly positive culture, per Moreno et al. 2018. Culture complements histologic confirmation rather than replacing it.

Cycle chart findings that should prompt suspicion: Brown spotting at the expected time of menstruation or into the early part of the cycle can be clinically relevant. Unusual prolonged bleeding, atypical cycle patterns, and post-coital bleeding in the context of reproductive failure are all worth noting and communicating to the clinician evaluating for CE. These are not diagnostic, but they are the kinds of observations that change the pre-test probability and should prompt the biopsy conversation. Charting the cycle makes these patterns visible and documentable.

The biopsy is the answer. Everything else is the clinical question that gets you there.

CE, Recurrent Pregnancy Loss, and Implantation Failure

This is the section that matters most for the patient who has had multiple losses or failed transfers with no explanation offered.

The connection between CE and reproductive failure is documented across multiple study designs. The mechanism is endometrial receptivity disruption: the persistent inflammatory state alters the cytokine milieu, impairs the expression of endometrial receptivity markers, and interferes with the molecular signaling required for embryo implantation and early trophoblast invasion. The embryo, however normal its morphology, cannot implant into an inflamed endometrium the way it should, per Kitaya et al. 2015.

The prevalence data are consistent in direction if heterogeneous in magnitude. Cicinelli et al. evaluated 360 women with unexplained recurrent miscarriage and found CE in 57.8% (208/360) by hysteroscopy; of those with hysteroscopic findings, 91.3% were also positive on histology, confirming that the inflammatory signal seen hysteroscopically reflected a real pathologic finding at the tissue level. Positive endometrial cultures were obtained in 68.3% of hysteroscopy-positive cases, with common bacteria most frequently identified, per Cicinelli et al. 2013.

McQueen et al. evaluated 395 women in a recurrent pregnancy loss program using a standardized endometrial biopsy protocol. Overall CE prevalence in this cohort was 9%, with 7% in the recurrent early pregnancy loss group and 14% in those with fetal demise. The cure rate after antibiotic treatment was 100%. The subsequent cumulative live birth rate for the treated CE group was 88%, compared to a per-pregnancy live birth rate of 7% in those same patients before treatment, which rose to 56% per pregnancy after treatment, per McQueen et al. 2014.

The implantation failure data are similarly directional. In a cohort of 106 women with repeated unexplained implantation failure at IVF, Cicinelli et al. found CE in 66.0% by hysteroscopy and 57.5% by histology. Antibiotic treatment significantly improved subsequent reproductive outcomes: the live birth rate in the cured-CE group was 60.8% vs. 13.3% in the persistent-CE group (p=0.02), per Cicinelli et al. 2015.

A 2022 systematic review and meta-analysis by Vitagliano et al. pooled data from ten studies covering 4,145 patients. Women with CE had significantly lower ongoing pregnancy and live birth rates compared to those without CE. After CE resolution with antibiotic treatment, ongoing pregnancy and live birth rates were comparable to unaffected patients. The effect of severe CE was more pronounced than mild CE, but the direction was consistent: untreated CE is a reproducible negative predictor of reproductive outcome, per Vitagliano et al. 2022.

What this evidence means in practice: a woman who has experienced two or more pregnancy losses, or who has had repeated implantation failure with no identified cause, and who has not had an endometrial biopsy with CD138 IHC, has not completed a full workup. The diagnosis may be sitting in the tissue that was never sampled.

A dedicated guide to miscarriage and recurrent pregnancy loss covers the full RPL workup and the RRM approach to unexplained losses.

Both partners matter. Male factor is solely responsible in 20 to 30% of couples with reproductive failure and contributes in another 20 to 30%. Evaluating the male partner with a full semen analysis is part of the complete workup. A CE diagnosis in the female partner does not close the investigation on the male side.

Treatment

CE is treated with antibiotic therapy. This is the established and evidence-supported approach, per Puente et al. 2019. Doxycycline is one of the most frequently studied antibiotic regimens in the CE literature, often used as first-line or as part of combination protocols. The specific regimen, duration, and any combination therapy are decisions made by the treating clinician based on the individual patient's microbiological culture results, organism sensitivities, and clinical context. No dosing guidance belongs on this page. This is a prescribing decision.

In specialist centers and several published cohorts, notably McQueen 2014, a post-treatment retest biopsy is performed to confirm resolution. The goal is not just treatment but confirmed resolution: a follow-up endometrial biopsy with CD138 IHC, performed after the antibiotic course, confirms whether the plasma cell infiltration has resolved. This practice is not yet a universal guideline standard, but it is the protocol that produces the strongest outcome data. If CE persists after a first course, a second course or a different antibiotic regimen may be indicated based on culture-guided sensitivity data.

Partner treatment depends on the organism identified. For Mycoplasma genitalium, simultaneous treatment of the male partner has clear evidence and guideline support: this organism behaves as a sexually transmitted pathogen, and an untreated partner risks reintroducing the infection. For Ureaplasma urealyticum and Mycoplasma hominis, the evidence for partner treatment is weaker, and major STI guidelines do not mandate it. Many clinicians specializing in infertility and CE do empirically treat the male partner when these organisms are cultured, particularly in the setting of recurrent reproductive failure, but this is a judgment call, not a protocol requirement. The treating clinician is the right person to make that call based on the individual culture results and clinical picture.

Treatment changes outcomes. The evidence reviewed in the previous section points consistently in the same direction: treating CE resolves the inflammatory state, and resolution is associated with improved pregnancy and live birth rates. The mechanism makes biological sense. The endometrium returns to a normal inflammatory baseline. Implantation can proceed in a receptive environment rather than an inflamed one.

One clinical caution on the literature: treatment regimens in published CE studies vary substantially across centers. There is no single universally agreed-upon protocol, and practice variation is real. The OPTIMUM treatment protocol (Kuroda et al. 2021), which addresses CE alongside thyroid dysfunction, thrombophilia, and immune factors, demonstrated improved pregnancy outcomes in RPL patients when CE was addressed as part of a multi-factor workup, per Kuroda et al. 2021. This illustrates that CE in the RPL population rarely exists in complete isolation: it is one diagnostic finding in a workup that should be looking at the full picture.

Outcomes After Treatment

The outcome data for CE treatment are encouraging. They are also heterogeneous, and that honesty belongs in this section.

The most consistent finding across studies is directional: treating CE improves reproductive outcomes compared to not treating it. The McQueen et al. cohort showed a cumulative live birth rate of 88% in treated patients, compared to a per-pregnancy live birth rate of 7% before treatment in those same patients. The Cicinelli et al. 2013 cohort showed significantly higher subsequent pregnancy success rates in women whose CE resolved versus those in whom it did not. The Vitagliano et al. 2022 meta-analysis showed that CE cure normalized outcomes to levels comparable to unaffected patients.

The heterogeneity in the literature is real and worth naming. Prevalence estimates vary widely because studies use different diagnostic thresholds for plasma cell counts on IHC, different histologic protocols, and different patient populations. Some studies use hysteroscopy as the primary diagnostic modality; others use histology; others use both. The threshold at which CE is called "positive" is not standardized across centers. This means the absolute prevalence numbers cited in different papers are not always directly comparable.

Similarly, treatment protocols vary. Doxycycline regimens differ in duration. Some centers add a second antibiotic. Some culture-guide therapy; others treat empirically. This variation means that "CE treatment" in one study is not identical to "CE treatment" in another.

What the evidence does support, consistently: the presence of CE is a negative predictor of reproductive success, its absence is not, and treatment-induced resolution is associated with improved outcomes. For a patient with recurrent loss or implantation failure and an untested endometrium, that is clinically meaningful. It means there is a diagnosable, treatable possibility that has not been excluded.

When to Suspect Chronic Endometritis

CE has no pathognomonic symptom. Its subclinical character is part of its clinical danger. But there are patterns worth recognizing.

History patterns that should prompt CE evaluation:

Repeated implantation failure after embryo transfer, particularly when embryo quality has been assessed as adequate and no structural uterine abnormality has been found. Two or more failed transfers in this context raises the pre-test probability of CE substantially.

Recurrent pregnancy loss without an identified cause. If the standard RPL workup (karyotype, thrombophilia, uterine anatomy, thyroid) has been completed and returned non-explanatory results, CE is an active diagnostic possibility that deserves investigation. The question is simple: has an endometrial biopsy with CD138 IHC been done? If not, it has not been excluded.

Persistent brown spotting at the end of cycles or into the early cycle days. This is not specific to CE, but it is a charted observation that accumulates clinical value when combined with a history of reproductive failure. It reflects atypical endometrial shedding and can be a downstream expression of the inflammatory state.

Unusual or prolonged menstrual bleeding with no structural cause identified on imaging. Again, not specific, but noteworthy in context.

Post-procedural history. Women who have had dilation and curettage (D&C) for miscarriage management, uterine instrumentation for polyp removal, or retained products of conception have had entry points for bacterial colonization. CE has been documented following these procedures.

Any patient told she has no fixable cause for repeated pregnancy loss or implantation failure should ask, explicitly: has CE been evaluated with an endometrial biopsy and CD138 staining? If the answer is no, that answer matters.

Acute Endometritis: A Brief Note

This guide is about chronic endometritis. Acute endometritis is a different clinical entity.

Acute endometritis is a symptomatic infection of the uterine lining, typically occurring after childbirth (postpartum endometritis), after pregnancy loss managed by D&C, or following uterine instrumentation. It presents with fever, uterine tenderness, and abnormal discharge. It is caused by ascending polymicrobial infection, is treated with systemic antibiotics, and is generally diagnosed and managed within the acute care setting.

Acute endometritis is mainstream territory. It is recognized, it is symptomatic, and it is treated. The diagnostic and management gaps that define CE do not apply to acute endometritis in the same way.

A woman who had acute endometritis after a delivery or procedure may subsequently develop CE as a sequela, but the two diagnoses are distinct and occur on different timescales. If you are experiencing fever, pelvic pain, and abnormal discharge in the postpartum period or after a procedure, seek evaluation through your obstetric or gynecologic provider. That is not what this page is about.

Preparing for a Consult

If you have had recurrent pregnancy loss or repeated implantation failure and CE has not been evaluated, here is what to bring to the conversation.

Operative and procedure reports. If you have had hysteroscopy, D&C, or any uterine procedure, request the full operative report, not just a summary. The report tells a clinician what was seen, how the uterine cavity looked, and whether any biopsy was taken. If a biopsy was taken, request the pathology report: it should specify whether CD138 IHC was included and whether plasma cells were identified.

IVF records. If you have had IVF cycles, the embryo transfer records describe embryo quality at the time of transfer. If transfers repeatedly failed with good-quality embryos and no endometrial biopsy was done before or between cycles, that is the gap to name explicitly.

Cycle charts. Charted cycles create a documented record of spotting patterns, bleeding character, cycle length variation, and any atypical symptom timing. If you have been charting, bring that record. If you have not been charting, starting now will give a clinician observable data.

The question to ask directly: Has CE been evaluated with an endometrial biopsy and CD138 immunohistochemistry? Not: has my uterus been looked at. Not: was my bloodwork normal. Specifically: has the endometrium been biopsied and the specimen stained for CD138?

If the answer is no, that is the starting point.

Frequently Asked Questions