Endometrial microbiota in infertile women with and without chronic endometritis as diagnosed using a quantitative and reference range-based method

Endometrial factors and pregnancy loss frequency in recurrent pregnancy loss patients: comparing RT-PCR microbiology, microbial cultures, and immunohistochemistry of endometrium biopsy

The objective of this study is to investigate the presence of bacteria in endometrial samples from patients with recurrent pregnancy loss (RPL) and explore potential correlations between bacterial presence, chronic endometritis, and previous pregnancy loss history. Endometrial samples from 90 RPL patients were analysed using RT-PCR to detect 10 specific bacterial species. A subgroup of 65 patients underwent additional microbial culture and immunohistochemistry for plasma cell identification. Correlations between bacterial presence, chronic endometritis, and the number of previous pregnancy losses were evaluated. We detected at least one out of 10 chosen bacteria DNA by RT-PCR in 24.4% (22/90) of endometrial samples. Patients with PCR-identified bacteria had a significantly higher number of previous pregnancy losses (median 3 vs 2, p = 0.01). No correlation was observed between bacterial presence and chronic endometritis diagnosis. A significant correlation was found between bacterial detection by PCR and microbial culture (p = 0.03), though culture methods detected fewer positive cases. In RPL patients, detecting DNA from at least one of 10 selected bacterial species by RT-PCR correlates with a higher number of previous pregnancy losses. However, this bacterial presence does not correlate with chronic endometritis diagnosis based on the CD138 immunohistochemistry-identified plasma cell count. These findings suggest a potential role of endometrial bacteria in RPL that may be independent of the classical inflammatory response associated with chronic endometritis.

Correlation between Lactobacillus of Vaginal Microbiota and the Pregnancy Outcomes for Patients Experiencing Recurrent Miscarriage

The etiology of recurrent miscarriage (RM) is complex, with the vaginal microbiota (VM) being an important factor associated with RM. We aimed to establish the VM composition in both patients with RM and healthy women and further investigate relationship between the subsequent pregnancy outcomes of patients with RM and VM, to explain the potential mechanism of VM in RM to some extent. A cohort study compared the VM between 34 patients with RM and 15 healthy women using a sequencing technique based on Type IIB restriction enzymes for the microbiome (2bRAD-M). Further comparison was made between 11 patients with clinical miscarriages (CM) and 13 patients with ongoing pregnancies (OP) in the RM group who conceived naturally. To determine the VM composition, the 2bRAD-M library was prepared, and sequence and bioinformatics analyses were conducted. The composition of the VM exhibited notable differences between the non-RM and RM groups, with significant findings for alpha diversity (p < 0.05) and beta diversity (p = 0.01). Further analysis between the RM-OP and RM-CM groups revealed a significant difference in Lactobacillus (97.81% ± 2.71% vs. 53.37% ± 46.42%, p = 0.03). Other uncommon species, such as Cutibacterium acnes (C. acnes) (p = 0.04) were found significantly increase in the RM-CM group. Functional annotation analysis revealed 47 related signaling pathways between the two groups. The results of this study indicate that Lactobacillus is associated with subsequent miscarriages and that C. acnes is closely related to pregnancy outcomes of patients with RM.

Comparison of diagnostic tests for chronic endometritis and endometrial dysbiosis in recurrent implantation failure: Impact on pregnancy outcomes

Chronic endometritis (CE) and endometrial dysbiosis (ED) are major causes of recurrent implantation failure (RIF). CE is diagnosed via hysteroscopy or the endometrial CD138 test; ED is examined using endometrial microbiome testing with next-generation sequencing. ED is characterized by a reduction in Lactobacillus species. However, correlations between the results of the three tests and the efficacy of treatment against CE and ED in pregnancy outcomes remain unclear. We analyzed 73 patients with RIF who underwent all three tests (hysteroscopy, endometrial CD138 test, and endometrial microbiome test). Patients with CE received antibiotics, whereas those with ED received antibiotics and vaginal Lactobacillus probiotics. The incidences of CE diagnosed using hysteroscopy and the CD138 test were 56.2 and 49.3%, respectively, and the prevalence of ED was 53.4%. No correlations were observed among the test-positive individuals in these three tests. Among patients with ED, 88.9% had a post-treatment clinical pregnancy, a significantly higher rate than that in patients without ED (p = 0.021). Multivariate analysis demonstrated that ED was associated with clinical pregnancy (odds ratio (OR): 6.29, p = 0.031). In conclusion, the three tests detected different populations of patients with RIF. ED diagnosed using the endometrial microbiome test was associated with favorable pregnancy outcomes after testing.

Lactobacillus Genus Complex Probiotic-Induced Changes on the Equine Clitoral Microbiome

Dysbiosis of the lower reproductive tract (LRT) in mares may play a role in clinical diseases, including endometritis and placentitis. Metagenomic/metagenetic analysis of bacterial DNA can identify organisms that are not readily cultured and, thus, may go undetected. In this study, we tested the following hypotheses: (1) the clitoris of estrual mares harbors a unique resident microbiome, (2) topical Lactobacillus genus complex (LGC)-containing probiotic will alter the equine clitoral microbiome, and (3) early pregnancy rates following clitoral LGC application will not differ significantly from industry standards. Mares (n = 12) in estrus had sterile clitoral swabs collected (0) prior to daily topical LGC for 4 days. Second (12 h) and third clitoral swabs (48 h) were collected following final LGC application. During the next estrus, the mares were bred by artificial insemination. Genomic DNA was extracted and used for 16S rRNA sequencing via the Illumina Miseq platform. Abundance was evaluated via Friedman test with pairwise Dunn's post hoc comparisons. Statistical significance was set at p < 0.05. Compared to time 0, Desulfobacterota decreased and Corynebacterium spp. increased at 12 h and 48 h compared to 0, while Actinobacillus and Fusobacterium spp. increased in a time-dependent manner. Furthermore, Mobiluncus spp. and Christensenellacea_R-7_group decreased at 12 h and 48 h compared to 0. LGC changed the beta but not alpha diversity at both 12 h and 48 h. Mares with LGC application achieved an 85% pregnancy rate in the subsequent estrus. Future investigations are needed to understand the role of the LRT microbiome and probiotics in equine breeding.

The reproductive tract microbiome in women with polycystic ovary syndrome and across different menstrual cycle phases

STUDY QUESTION

Do polycystic ovary syndrome (PCOS), menstrual cycle phases, and ovulatory status affect reproductive tract (RT) microbiome profiles?

SUMMARY ANSWER

We identified microbial features associated with menstrual cycle phases in the upper and lower RT microbiome, but only two specific differences in the upper RT according to PCOS status.

WHAT IS KNOWN ALREADY

The vaginal and uterine microbiome profiles vary throughout the menstrual cycle. Studies have reported alterations in the vaginal microbiome among women diagnosed with PCOS.

STUDY DESIGN, SIZE, DURATION

This prospective case-control study included a cohort of 37 healthy control women and 52 women diagnosed with PCOS. Microbiome samples were collected from the vagina as vaginal swabs (VS) and from the uterus as endometrial flushing (EF) aspirate samples, and compared according to PCOS diagnosis, the menstrual cycle phases, and ovulatory status, at Oulu University Hospital (Oulu, Finland) from January 2017 to March 2020.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 83 VS samples and 80 EF samples were collected. Age and body mass index (BMI) were matched between women with and without PCOS. Clinical characteristics were assessed using blood samples collected between cycle days 2 and 8, and microbial DNA was sequenced on the Ion Torrent platform. Microbial alpha diversity (i.e. the observed number of unique genera and Shannon diversity index) was analysed across sample types, PCOS diagnosis and menstrual cycle phases. Linear mixed-effects models were utilised to identify microbial features in relation to PCOS and the menstrual cycle phases. Associations between the beta diversity of the RT microbiome and PCOS- and cycle-related clinical features were calculated using PERMANOVA.

MAIN RESULTS AND THE ROLE OF CHANCE

Microbial alpha diversity showed no difference with PCOS (VS: Pobserved feature = 0.836, Pshannon = 0.998; EF: Pobserved feature = 0.366, Pshannon = 0.185), but varied with menstrual cycle phases (VS: Pobserved feature = 0.001, Pshannon = 0.882; EF: Pobserved feature = 0.026, Pshannon = 0.048). No difference was observed in beta diversity based on either PCOS or the menstrual cycle phases (VS: PPCOS = 0.280, Pcycle = 0.115; EF: PPCOS = 0.234, Pcycle = 0.088). In the endometrial flushing samples, we identified two novel microbial features, characterised by the ratio of differential abundance of two genera, associated with PCOS (FDR ≤ 0.1) and 13 novel features associated with the menstrual cycle phases (FDR ≤ 0.1).

LIMITATIONS, REASONS FOR CAUTION

Although this was the first study to simultaneously analyse, the lower and upper RT microbiome in women with and without PCOS, the limited sample size of anovulatory cases may hinder the detection of differences related to PCOS and ovulatory status.

WIDER IMPLICATIONS OF THE FINDINGS

The main finding suggests that PCOS and the menstrual cycle phases are associated with specific microbial features in the upper RT, indicating that the analysis of the upper RT microbiome can potentially identify biomarkers for both PCOS and menstrual cycle phases.

STUDY FUNDING/COMPETING INTEREST(S)

This research was funded by the Research Council of Finland (grants no. 315921, 321763, 336449), the Sigrid Jusélius Foundation, Novo Nordisk Foundation (grant no. NNF21OC0070372), and the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant (MATER, grant no. 813707). This research was also funded by the Estonian Research Council (grants no. PRG1076, PRG1414), the Horizon Europe grant (NESTOR, grant no. 101120075) of the European Commission, and EMBO Installation Grant (grant no. 3573). The funders did not participate in any processes of the study. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

All Properties of Infertility Microbiome in a Review Article

BACKGROUND

The microbiome is crucial for many physiological processes, including immunity, metabolism, and reproduction.

AIMS

This review aims to contribute to a detailed understanding of the microbiome of the genital tract, which can lead to better management of dysbiosis and reproductive disorders.

METHODS

Data from the four international information databases Medline, Scopus, Embase, and Google Scholar. The search strategy was based on the combination of the following terms: "microbiota," "microbiome," "microfilm," "microflora," "fertility," or "infertility."

RESULT

The advent of next-generation sequencing-based technologies during the last decade has revealed the presence of microbial communities in nearly every part of the human body, including the reproductive system. Several studies have shown significant differences between the microbiota of the vagina and endometrium, as well as other parts of the upper genital tract.

DISCUSSION

The human microbiome plays a critical role in determining a person's health state, and the microbiome of the genital tract may impact fertility potential before and after assisted reproductive treatments (ARTs).

CONCLUSION

To completely understand the role of the microbiome, future research should focus not only on the description of microbiota but also on the interaction between bacteria, the production of biofilms, and the interaction of microorganisms with human cells.

Uterine Microbiota and Bisphenols: Novel Influencers in Reproductive Health

Infertility affects 8-12% of couples worldwide, and 30-75% of preclinical pregnancy losses are due to a failure during the implantation process. Exposure to endocrine disruptors, like bisphenols, among others, has been associated with the increase in infertility observed in the past decades. An increase in infertility has correlated with exposure to endocrine disruptors like bisphenols. The uterus harbors its own microbiota, and changes in this microbiota have been linked to several gynecological conditions, including reproductive failure. There are no studies on the effects of bisphenols on the uterine-microbiota composition, but some inferences can be gleaned by looking at the gut. Bisphenols can alter the gut microbiota, and the molecular mechanism by which gut microbiota regulates intestinal permeability involves Toll-like receptors (TLRs) and tight junction (TJ) proteins. TJs participate in embryo implantation in the uterus, but bisphenol exposure disrupts the expression and localization of TJ proteins. The aim of this review is to summarize the current knowledge on the microbiota of the female reproductive tract (FRT), its association with different reproductive diseases-particularly reproductive failure-the effects of bisphenols on microbiota composition and reproductive health, and the molecular mechanisms regulating uterine-microbiota interactions crucial for embryo implantation. This review also highlights existing knowledge gaps and outlines research needs for future risk assessments regarding the effects of bisphenols on reproduction.

Chronic endometritis and fertility: A binomial linked by microorganisms

OBJECTIVES

To explore the relationship of microorganisms with chronic endometritis, comparing findings in our region with reports in the literature.

STUDY DESIGN

Retrospective descriptive study of 110 endometrial biopsies from women treated for fertility problems at a tertiary hospital from 2021 through 2022. Results were compared between women with and without chronic endometritis.

RESULTS

Chronic endometritis was diagnosed in 50.91 % (n = 56) of the women, with at least one microorganism detected in 57.14 % (n = 32). Microorganisms other than Lactobacillus spp. were more often (p = 0.009) observed in women with chronic endometritis. The most frequently isolated non-Lactobacillus microorganism was Gardnerella vaginalis (10.71 %), followed by Streptococcus anginosus (8.93 %), S. agalactiae (5.36 %), and Corynebacterium amycolatum (5.36 %). There was a trend towards a lower frequency of Lactobacillus spp. in women with chronic endometritis (p = 0.08672).

CONCLUSIONS

The endometrial microbiota significantly differs between women with versus without chronic endometritis, observing a reduced proportion of Lactobacillus spp. and proteobacteria and an increased proportion of Gardnerella spp. in the former. However, further research is needed on the relationship between microorganisms and chronic endometritis to assist therapeutic decision-making and improve the reproductive prognosis.

A comprehensive analysis of the uterine microbiome in endometrial cancer patients - identification of Anaerococcus as a potential biomarker and carcinogenic cofactor

Introduction

Endometrial cancer (EC) is a significant gynecological malignancy with increasing incidence worldwide. Emerging evidence highlights the role of the uterine microbiome in the pathogenesis of EC. This study aims to characterize the uterine microbiome in EC patients and identify potential microbial biomarkers, with a focus on Anaerococcus as a differentiating taxon.

Methods

The endocervical canal swabs from patients with EC (n=16) and non-cancerous patients (EM, n=13) were collected. The V3-V4 region of the 16S rRNA gene was sequenced using the Illumina platform. Bioinformatic analyses were performed with QIIME2, and statistical comparisons were conducted to assess differences in microbial composition and diversity. In vitro experiments were conducted to assess the functional impact of Anaerococcus on human uterine fibroblasts, including its ability to adhere to the human cells and induce oxidative stress.

Results

The α-diversity metrics, including Shannon entropy and observed amplicon sequence variants (ASVs), revealed significantly higher microbial diversity in EC samples compared to EM. Anaerococcus was identified as a key taxon differentiating EC from EM groups, showing a higher relative abundance in EC samples. Functional predictions and in vitro assays indicated that Anaerococcus may contribute to carcinogenesis by inducing reactive oxygen species (ROS) production, and has the high ability to adhere to the human endometrial fibroblasts.

Discussion

The study provides evidence of distinct microbial signatures in EC, with Anaerococcus emerging as a potential biomarker. The in vitro findings suggest its role in endometrial carcinogenesis, underscoring its potential as a target for future diagnostic and therapeutic applications.

Methodological approaches in 16S sequencing of female reproductive tract in fertility patients: a review

BACKGROUND

The female genital tract microbiome has become a particular area of interest in improving assisted reproductive technology (ART) outcomes with the emergence of next-generation sequencing (NGS) technology. However, NGS assessment of microbiomes currently lacks uniformity and poses significant challenges for accurate and precise bacterial population representation.

OBJECTIVE

As multiple NGS platforms and assays have been developed in recent years for microbiome investigation-including the advent of long-read sequencing technologies-this work aimed to identify current trends and practices undertaken in female genital tract microbiome investigations.

RESULTS

Areas like sample collection and transport, DNA extraction, 16S amplification vs. metagenomics, NGS library preparation, and bioinformatic analysis demonstrated a detrimental lack of uniformity. The lack of uniformity present is a significant limitation characterised by gap discrepancies in generation and interpretation of results. Minimal consistency was observed in primer design, DNA extraction techniques, sample transport, and bioinformatic analyses.

CONCLUSION

With third-generation sequencing technology highlighted as a promising tool in microbiota-based research via full-length 16S rRNA sequencing, there is a desperate need for future studies to investigate and optimise methodological approaches of the genital tract microbiome to ensure better uniformity of methods and results interpretation to improve clinical impact.

"Shortening time to pregnancy in infertile women by personalizing treatment of microbial imbalance through Emma & Alice: A multicenter prospective study"

Purpose

To evaluate the impact of Endometrial Microbiome Metagenomic Analysis and Analysis of Infectious Chronic Endometritis (EMMA & ALICE) on pregnancy outcomes following recommended treatments in women with recurrent implantation failure (RIF) or recurrent pregnancy loss (RPL).

Methods

This prospective, multicenter cohort study included 527 women under 42 years old with RIF or RPL across 14 IVF centers in Japan. Endometrial samples were analyzed using EMMA & ALICE, and patients received antibiotics, probiotics, or no treatment based on test results. Pregnancy outcomes were assessed using Kaplan-Meier survival analysis and multivariate generalized linear models.

Results

Amongst participants, 43.4% had a normal Lactobacillus-dominated microbiota, 20.9% had dysbiosis, and 35.7% had mild dysbiosis or ultralow biomass. Kaplan-Meier analysis revealed significantly higher ongoing pregnancy rates in the dysbiosis group treated with antibiotics and probiotics compared to other groups (p = 0.031). Post-treatment, ongoing pregnancy rates in the dysbiosis and mild dysbiosis groups were comparable to the normal group.

Conclusions

EMMA & ALICE-guided antimicrobial and probiotic treatments improved pregnancy outcomes, enabling the dysbiosis group to achieve pregnancy earlier than the normal group. Addressing uterine dysbiosis may reduce the time to pregnancy in patients with RIF and RPL.

Trial registration

University Hospital Medical Information Network (UMIN), UMIN000036917.

Differential characteristics of vaginal versus endometrial microbiota in IVF patients

Abnormal female reproductive tract microbiota are associated with gynecological disorders such as endometriosis or chronic endometritis and may affect reproductive outcomes. However, the differential diagnostic utility of the vaginal or the endometrial microbiome and the impact of important technical covariates such as the choice of hypervariable regions for 16 S rRNA sequencing remain to be characterized. The aim of this retrospective study was to compare vaginal and endometrial microbiomes in IVF patients diagnosed with implantation failure (IF) and/or recurrent pregnancy loss (RPL) and to investigate the overlap between established vaginal and endometrial microbiome classification schemes. An additional aim was to characterize to which extent the choice of V1-V2 or V2-V3 16 S rRNA sequencing schemes influences the characterization of genital microbiomes. We compared microbiome composition based on V1-V2 rRNA sequencing between matched vaginal smear and endometrial pipelle-obtained biopsy samples (n = 71); in a sub-group (n = 61), we carried out a comparison between V1-V2 and V2-V3 rRNA sequencing. Vaginal and endometrial microbiomes were found to be Lactobacillus-dominated in the majority of patients, with the most abundant Lactobacillus species typically shared between sample types of same patient. Endometrial microbiomes were found to be more diverse than vaginal microbiomes (average Shannon entropy = 1.89 v/s 0.75, p = 10-5) and bacterial species such as Corynebacterium sp., Staphylococcus sp., Prevotella sp. and Propionibacterium sp. were found to be enriched in the endometrial samples. The use of two widely used clinical classification schemes to detect microbiome dysbiosis in the reproductive tract often led to inconsistent results vaginal community state type (CST) IV, which is associated with bacterial vaginosis, was detected in 9.8% of patients; however, 31,0% of study participants had a non-Lactobacillus-dominated (NLD) endometrial microbiome associated with unfavorable reproductive outcomes. Results based on V2-V3 rRNA sequencing were generally consistent with V1-V2-based; differences were observed for a small number of species, e.g. Bifidobacterium sp., Propionibacterium sp. and Staphylococcus sp. and with respect to slightly increased detection rates of CST IV and NLD. Our study showed that endometrial microbiomes differ substantially from their vaginal counterparts, the application of a trans-cervical sampling method notwithstanding. Characterization of endometrial microbiomes may contribute to the improved detection of women with an unfavorable reproductive outcome prognosis in IVF patients..

Pharmacological and non-pharmacological interventions for improving endometrial receptivity in infertile patients with polycystic ovary syndrome: a comprehensive review of the available evidence

Direct and indirect evidence suggests that endometrial receptivity may play a crucial role in the reduced fertility rate of women with polycystic ovary syndrome (PCOS). Various pharmacological and non-pharmacological strategies with potential effects on endometrial receptivity in patients with PCOS have been proposed. The aim of this study was to summarize the rationale and the clinical and experimental evidence of interventions tested for improving endometrial receptivity in infertile patients with PCOS. A systematic review was conducted by consulting electronic databases. All interventions with a potential influence on endometrial receptivity in infertile patients with PCOS were evaluated, and their main biological mechanisms were analysed. In total, 24 interventions related to endometrial receptivity were identified. Notwithstanding a strong biological rationale, no intervention aimed at improving endometrial receptivity in women with PCOS is supported by an adequate body of evidence, limiting their use in clinical practice. Further high-quality research is needed in this field to limit potentially ineffective and unsafe add-on treatments in infertile patients with PCOS.

Mechanism of Endometrial Receptivity Affected by Fibroids

Fibroids are the most common benign tumors of the female reproductive system. Most patients with fibroids are asymptomatic, but the presence of fibroids can still cause some abnormal clinical symptoms, such as increased menstrual volume, abnormal uterine bleeding, pelvic pain, urinary tract and gastrointestinal tract compression symptoms, etc. The impact of fibroids on pregnancy is worth discussing. At present, it is believed that submucosal myoma and intramural myoma affecting uterine cavity shape affect the pregnancy outcome of patients, while the impact of type III intramural myoma on pregnancy is still controversial. A number of studies have found that in addition to direct contact with the endometrial compression, uterine myoma also affects the endometrial flexibility through other ways. In this review, we summarized the effects of fibroids on endometrial receptivity and discussed in depth the mechanisms of such effects, including secretion of cytokines, changes in endometrial blood flow and angiogenesis, effects on endometrial peristalsis and mechanical stress conduction, changes in uterine microecological environment, and abnormal signal transduction pathways. Understanding the mechanism of endometrial receptivity affected by fibroids is significant for exploring the treatment of fibroids, improving the pregnancy outcome of patients with fibroids and increasing the clinical pregnancy rate.

Linking reproductive tract microbiota to premature ovarian insufficiency: Pathophysiological mechanisms and therapies

Over the past decade, research on the human microbiota has become a hot topic. Among them, the female reproductive tract (FRT) also has a specific microbiota that maintains the body's health and dynamic balance, especially in the reproductive aspect. When the FRT ecosystem is dysregulated, changes in immune and metabolic signals can lead to pathological and physiological changes such as chronic inflammation, epithelial barrier disruption, changes in cell proliferation and apoptosis, and dysregulation of angiogenesis and metabolism, thereby causing disruption of the female endocrine system. Premature ovarian insufficiency (POI), a clinical syndrome of ovarian dysfunction, is primarily influenced by immune, genetic, and environmental factors. New evidence suggests that dysbiosis of the FRT microbiota and/or the presence of specific bacteria may contribute to the occurrence and progression of POI. This influence occurs through both direct and indirect mechanisms, including the regulation of estrogen metabolism. The use of probiotics or microbiota transplantation to regulate the microbiome has also been proven to be beneficial in improving ovarian function and the quality of life in women with premature aging. This article provides an overview of the interrelationships and roles between the FRT microbiome and POI in recent years, to fully understand the risk factors affecting female reproductive health, and to offer insights for the future diagnosis, treatment, and application of the FRT microbiome in POI patients.

Altered Endometrial Microbiota Profile Is Associated With Poor Endometrial Receptivity of Repeated Implantation Failure

PURPOSE

To gain insight into the endometrial pathophysiology of unexplained repeated implantation failure (RIF), we examined the characteristics of genital tract microbiota and explored the correlation between the microbiota and endometrial receptivity.

METHODS

Vaginal secretion (VS) and endometrial biopsy (EB) samples were collected from patients with RIF (RIF group, n = 32) and those with infertility who had achieved pregnancy during their initial embryo transfer cycle (control group, n = 18). 16S ribosomal RNA sequencing and quantitative PCR were performed to characterize the microbiota of the two groups. Spearman's correlation analysis was performed to determine the relationship between endometrial receptivity markers and endometrial microbiota.

RESULTS

Endometrial microbiota exhibited distinct characteristics from vaginal microbiota, with a higher alpha-diversity. Alpha-diversity of the endometrial microbiota was higher in the RIF group than in the control group. Compared with the control group, the RIF group had a significant decrease in endometrial Lactobacillus abundance and an increase in Gardnerella and Acinetobacter abundances. The expression levels of endometrial receptivity markers, including homeobox A11, integrin αvβ3, leukemia inhibitor factor, matrix metalloproteinase-9, and vascular endothelial growth factor, were lower in the RIF group than in the control group. Moreover, the expression levels of these markers were correlated with endometrial Lactobacillus, Gardnerella, and Acinetobacter abundances.

CONCLUSION

RIF is characterized by endometrial microbiota dysbiosis and poor endometrial receptivity. Moreover, abnormal endometrial microbiota is associated with impaired endometrial receptivity, which may be a potential cause of unexplained RIF.

The role and challenges of regulating endometrial microbiome in uterine health and diseases

The uterine environment provides necessary conditions for the existence of endometrial microbiota, which in turn plays an important role in maintaining the homeostasis of the uterine environment. The endometrial microbiome is highly susceptible to external factors such as age, hormones, menstrual, pregnancy, etc. When the microbiota is imbalanced, it will further promote the occurrence of uterine diseases such as endometritis and endometrial cancer. Regulating the microbiome of the endometrium is of positive significance for promoting uterine health. Among them, antibiotics, probiotics, prebiotics, and microbial transplantation may be important pathways for regulating endometrial microbiota in the future. However, there is currently no unified plan for evaluating the endometrial microbiota. In addition, due to the small sample size, it is easy to be contaminated by exogenous bacterial DNA, which poses great challenges for studying the mechanism of microbial community regulating uterine health. Therefore, there are still many areas worth exploring for the future of endometrial microbiome.

Correlation of hysteroscopic findings of chronic endometritis with CD138 immunohistochemistry and their correlation with pregnancy outcomes

PURPOSE

To investigate the correlation between hysteroscopic findings of chronic endometritis and CD138 immunohistochemistry positive in endometritis and to analyze the pregnancy outcomes and associated risk factors following embryo transfer in women diagnosed with chronic endometritis via hysteroscopy.

METHODS

A retrospective observational study carried out at the Reproductive Medicine Center of Tangdu Hospital of Air Force Medical University, from January 2021 to December 2021, was performed by obtaining data from 194 medical records of women who underwent hysteroscopies for infertility and were diagnosed with chronic endometritis based on Delphi criteria. Spearman correlation analysis was used to evaluate the correlation between hysteroscopic findings and endometrial CD138 immunohistochemistry. The study also observed the differences in relevant indexes between the CD138-positive and CD138-negative groups after embryo transfer and analyzed factors influencing implantation failure using logistic regression analysis.

RESULTS

The correlation analysis between hysteroscopic findings and CD138 immunohistochemistry showed that micropolyps were correlated with CD138 immunohistochemistry positivity. The correlation coefficient was 0.32 (P < 0.01). After embryo transfer, the clinical pregnancy rate of the CD138-positive group was lower compared to that of the CD138-negative group [64.79% (46/71) vs. 81.30% (100/123), P < 0.05]. The results of the multivariate logistic regression analysis revealed that age (P = 0.43) and CD138 immunohistochemistry positivity (P = 0.008) were the independent risk factors for predicting whether or not embryo implantation was successful.

CONCLUSION

Hysteroscopic findings do not correlate strongly with endometrial CD138 immunohistochemistry, and chronic endometritis cannot be diagnosed by hysteroscopy alone. CD138 immunohistochemistry positivity is an independent factor contributing to the decrease in clinical pregnancy rate following embryo transfer.

Uterine Endometrium Microbiome in Women with Repeated Implantation Failure Complicated by Endometriosis

Objectives: This prospective study evaluated whether endometriosis is associated with chronic endometritis (CE) and affects the uterine endometrium microbiome (UEM) in women with repeated implantation failure (RIF). Methods: Forty-three women with RIF were divided into 12 with endometriosis (EM) and 31 without endometriosis (non-EM). The UEM was examined by 16S ribosomal RNA (rRNA) sequencing, and CE was determined by CD 138 staining (plasma cells > 5.15/10 mm2) simultaneously. Results: The EM group had a higher bacterial number (EM vs. non-EM; median [range], 6.5 vs. 3 [3-11, 1-16], p = 0.009), while the frequency of Lactobacillus species did not change. The rates of presence of Dialister (41.7% [5/12] vs. 3.3% [1/31], p = 0.004) and Streptococcus species (58.3% [7/12] vs. 16.1% [5/31], p = 0.017) were higher in the EM group. The prevalence of CE did not differ between the two groups. Multivariable logistic regression analysis revealed that the presence of Dialister species (odds ratio, 10.97, 95% confidence interval, 1.17-249.37, p = 0.036) was associated with endometriosis. In the EM group, five women with Dialister species had a higher number of bacterial species (10 vs. 5 [6-11, 3-7], p = 0.021) and higher Shannon diversity index (0.50 vs. 0.20 [0.19-1.39, 0.03-0.46], p = 0.026) than seven without Dialister species. Conclusions: Dialister and Streptococcus species, and the increased number of bacterial species in UEM may be related to the pathogenesis of RIF complicated by endometriosis.

A Standard Pipeline for Analyzing the Endometrial Microbiome

The endometrial microbiome is a rapidly advancing field of research, particularly in obstetrics and gynecology, as it has been found to be linked with obstetric complications and potential impacts on fertility. The diversity of microorganisms presents in the endometrium, along with their metabolites, can influence reproductive outcomes by modulating the local immune environment of the uterus. However, a major challenge in advancing our understanding of the endometrial microbiota lies in the heterogeneity of available studies, which vary in terms of patient selection, control groups, collection methods and analysis methodologies. In this study, we propose a detailed pipeline for endometrial microbiome analysis, based on the most comprehensive prospective of 64 studies that have investigated the endometrial microbiome up to the present. Additionally, our review suggests that a dominance of Lactobacilli in the endometrium may be associated with improved reproductive prognosis, including higher implantation rates and lower miscarriage rates. By establishing a standardized pipeline, we aim to facilitate future research, enabling better comparison and correlation of bacterial communities with the health status of patients, including fertility-related issues.

Chronic endometritis and the endometrial microbiota: implications for reproductive success in patients with recurrent implantation failure

BACKGROUND

Chronic endometritis (CE) is associated with poor reproductive outcomes, yet the role of endometrial microbiota in patients with recurrent implantation failure (RIF) and CE remains unclear. This study aims to characterize endometrial microbiota in RIF patients with CE and assess its implications for reproductive outcomes.

METHODS

In this prospective study, we enrolled RIF patients both with and without CE. Endometrial and cervical samples were collected for 16 S rRNA gene sequencing. Microbiota composition was compared between groups using diversity indices, phylum, and genus-level analysis. Canonical correlation analysis (CCA) and Spearman's correlation coefficients were used to assess relationships between CE, reproductive outcomes, and microbiota. Predictive functional profiling was performed to evaluate metabolic pathways associated with CE.

RESULTS

Endometrial microbiota in CE patients exhibited greater diversity and evenness compared to non-CE patients. Principal coordinates analysis (PCoA) revealed distinct clustering between CE and non-CE groups. Linear discriminant analysis (LDA) identified Proteobacteria, Aminicenantales, and Chloroflexaceae as characteristic of CE, while Lactobacillus, Acinetobacter, Herbaspirillum, Ralstonia, Shewanela, and Micrococcaceae were associated with non-CE. CCA demonstrated associations between CE, adverse reproductive outcomes, and specific bacterial taxa. Microbial metabolic pathways significantly differed between CE and non-CE groups, with enrichment in pathways related to cofactors, vitamins, secondary metabolites, and the immune system in CE patients.

CONCLUSION

RIF patients with CE exhibit distinct endometrial microbiota compositions associated with adverse reproductive outcomes. The increased microbial diversity and altered metabolic pathways in CE suggest a potential correlation with reproductive outcomes, although further studies are necessary to elucidate the causal relationship between microbiota alterations and fertility. Modulating the endometrial microbiome may represent a novel therapeutic strategy to improve IVF outcomes in patients with CE.

Understanding the Role of Female Genital Tract Microbiome in Recurrent Implantation Failure

The realization of the role of the microbiome of the female reproductive tract in health and disease has opened numerous possibilities for the scientific examination of the intertwining role between the human host and its microbiota. The imbalance in the composition of the microbial communities of the vagina and uterus is now recognized as a risk factor for many complications in pregnancy and according to the data from numerous studies, it is possible for this imbalance to play a crucial role in creating a hostile endometrial environment, and therefore, contributing to the etiology of recurrent implantation failure. Nevertheless, our current understanding of these complicated biological phenomena is far from complete, and in the future, there needs to be a systematic and thorough investigation of the diagnosis and therapy of this condition. This will enable scientists who engage in the field of assisted reproduction technologies to accurately identify and cure women in whom dysbiosis hinders the achievement of a healthy pregnancy.

Correlation between hysteroscopic features and specific microbial species in women with chronic endometritis

Objective and rationale

Chronic endometritis (CE) has recently been associated with unexplained infertility and recurrent miscarriages. The current gold standard for CE detection is histopathological examination. However, office hysteroscopy and endometrial cultures are also significant, due to the possible link between CE and various microorganisms. Bacterial colonization of the endometrium has been associated with reduced success rates of in vitro fertilisation embryo transfer. Few studies have tried to correlate CE hysteroscopy findings with pathogenic microorganisms. This prospective cohort study sought to establish whether hysteroscopic diagnostic lesions correlate with specific microbial species.

Methods

The study encompassed women undergoing diagnostic tests for a range of subfertility health issues. 189 women completed the standard office diagnostic hysteroscopy (DH). 181 had also endometrial samples taken for microbial culture investigation. Correlation analysis (χ2 and Fisher's exact test) between hysteroscopic findings suggestive of CE and endometrial cultures was carried out. Logistic regression models were also fitted to measure whether a positive endometrial culture could affect CE conditions.

Results

A significant association of E. coli was observed between the hysteroscopically characterized CE + group with focal hyperplasia, when compared to the non-CE group. Logistic regression analysis revealed that women positive for E. coli were 4.423 times more likely to have focal endometrial hyperplasia. No other significant correlations were identified between DH and positive endometrial cultures.

Conclusions

The presence of E. coli in the endometrium was significantly correlated with focal hyperplasia findings from hysteroscopy, emphasizing the importance of microbial cultures in the diagnosis and targeted treatment of CE in women with subfertility.

Distinct Gastrointestinal and Reproductive Microbial Patterns in Female Holobiont of Infertility

The microbiota is in symbiosis with the human body as a holobiont. Infertility conditions affect the female reproductive tract (FRT) and its resident microbiota. However, a disturbance in homeostasis could influence the FRT and other distal body sites, such as the gastrointestinal tract (GIT). We included 21 patients with endometriosis and other infertility-associated diseases with clinical profiles and biological samples from the FRT (endometrium, endometrial fluid, and vagina), and GIT samples (oral and feces). We performed a 16S rRNA analysis of site-specific microbial communities and estimated diversity metrics. The study found body site-specific microbial patterns in the FRT-GIT. In both study groups, Lactobacillus was the most shared Amplicon Sequence Variant (ASV), a precise identifier of microbial sequences, between endometrial and vagina samples. However, shared Gardnerella and Enterobacteriaceae ASVs were linked to other conditions but not endometriosis. Remarkably, Haemophilus was a specific GIT-shared taxon in endometriosis cases. In conclusion, infertility influences distinctly the FRT and GIT microbiomes, with endometriosis showing unique microbial characteristics. We proposed the concept of 'female holobiont' as a community that comprises the host and microbes that must maintain overall homeostasis across all body sites to ensure a woman's health. Insights into these microbial patterns not only advance our understanding of the pathophysiology of infertility but also open new avenues for developing microbe-based therapeutic interventions aimed at restoring microbial balance, thereby enhancing fertility prospects.

Microbiome in Female Reproductive Health: Implications for Fertility and Assisted Reproductive Technologies

The microbiome plays a critical role in the process of conception and the outcomes of pregnancy. Disruptions in microbiome homeostasis in women of reproductive age can lead to various pregnancy complications, which significantly impact maternal and fetal health. Recent studies have associated the microbiome in the female reproductive tract (FRT) with assisted reproductive technology (ART) outcomes, and restoring microbiome balance has been shown to improve fertility in infertile couples. This review provides an overview of the role of the microbiome in female reproductive health, including its implications for pregnancy outcomes and ARTs. Additionally, recent advances in the use of microbial biomarkers as indicators of pregnancy disorders are summarized. A comprehensive understanding of the characteristics of the microbiome before and during pregnancy and its impact on reproductive health will greatly promote maternal and fetal health. Such knowledge can also contribute to the development of ARTs and microbiome-based interventions.

The endometrial microbiota and early pregnancy loss

The human endometrium is a dynamic entity that plays a pivotal role in mediating the complex interplay between the mother and developing embryo. Endometrial disruption can lead to pregnancy loss, impacting both maternal physical and psychological health. Recent research suggests that the endometrial microbiota may play a role in this, although the exact mechanisms are still being explored, aided by recent technological advancements and our growing understanding of host immune responses. Suboptimal or dysbiotic vaginal microbiota, characterized by increased microbial diversity and reduced Lactobacillus dominance, has been associated with various adverse reproductive events, including miscarriage. However, the mechanisms linking the lower reproductive tract microbiota with pregnancy loss remain unclear. Recent observational studies implicate a potential microbial continuum between the vaginal and endometrial niche in patients with pregnancy loss; however, transcervical sampling of the low biomass endometrium is highly prone to cross-contamination, which is often not controlled for. In this review, we explore emerging evidence supporting the theory that a dysbiotic endometrial microbiota may modulate key inflammatory pathways required for successful embryo implantation and pregnancy development. We also highlight that a greater understanding of the endometrial microbiota, its relationship with the local endometrial microenvironment, and potential interventions remain a focus for future research.

The reproductive microbiome in dogs: Friend or foe?

The microbiome of the reproductive tract is an area of research in full development. Specifically, the microbiome may be involved in reproductive health, disease, and pregnancy outcomes, as has been shown in humans and animals, including dogs. The aim of the present review was to summarize current knowledge on the microbiome of the canine reproductive tract, to expose the controversial role that some bacterial agents may play in canine subfertility, and to highlight future research perspectives. This review discussed whether the use of antimicrobials in dogs is appropriate to increase reproductive performance and to treat subfertility without proper diagnosis, and the possible use of probiotics to modulate the reproductive canine microbiome. Finally, we indicate areas in which scientific knowledge is currently lacking, and could be promising directions for future research.

Deciphering the role of female reproductive tract microbiome in reproductive health: a review

Relevant studies increasingly indicate that female reproductive health is confronted with substantial challenges. Emerging research has revealed that the microbiome interacts with the anatomy, histology, and immunity of the female reproductive tract, which are the cornerstone of maintaining female reproductive health and preventing adverse pregnancy outcomes. Currently, the precise mechanisms underlying their interaction and impact on physiological functions of the reproductive tract remain elusive, constituting a prominent area of investigation within the field of female reproductive tract microecology. From this new perspective, we explore the mechanisms of interactions between the microbiome and the anatomy, histology, and immunity of the female reproductive tract, factors that affect the composition of the microbiome in the female reproductive tract, as well as personalized medicine approaches in managing female reproductive tract health based on the microbiome. This study highlights the pivotal role of the female reproductive tract microbiome in maintaining reproductive health and influencing the occurrence of reproductive tract diseases. These findings support the exploration of innovative approaches for the prevention, monitoring and treatment of female reproductive tract diseases based on the microbiome.

Oral Clostridium butyricum on mice endometritis through uterine microbiome and metabolic alternations

Endometritis occurs frequently in humans and animals, which can negatively affect fertility and cause preterm parturition syndrome. Orally administered Clostridium butyricum, a butyrate-producing gram-positive anaerobe, exhibits anti-inflammatory effects. However, the precise mechanism by which Clostridium butyricum attenuates endometritis remains unclear. This in vivo study evaluated the anti-inflammatory effects of orally administered Clostridium butyricum on uterine tissues. In addition, we conducted uterine microbiome and lipid metabolome analyses to determine the underlying mechanisms. Female Balb/c mice were divided into the following four groups (n = 5-20): (1) mock group, (2) only operation group (mice only underwent operation to exposed uterine horns from the side), (3) control group (mice underwent the same operation with the operation group + perfusion of lipopolysaccharide solution from uterine horns), and (4) Clostridium butyricum administration group (mice underwent the same operation with the control group + oral Clostridium butyricum administration from days 0 to 9). Clostridium butyricum was administered via oral gavage. On day 10, we investigated protein expression, uterine microbiome, and lipid metabolism in uterine tissues. Consequently, orally administered Clostridium butyricum altered the uterine microbiome and induced proliferation of Lactobacillus and Limosilactobacillus species. The effects can contribute to show the anti-inflammatory effect through the interferon-β upregulation in uterine tissues. Additionally, oral Clostridium butyricum administration resulted in the upregulations of some lipid metabolites, such as ω-3 polyunsaturated fatty acid resolvin D5, in uterine tissues, and resolvin D5 showed anti-inflammatory effects. However, the orally administered Clostridium butyricum induced anti-inflammatory effect was attenuated with the deletion of G protein-coupled receptor 120 and 15-lipooxgenase inhibition. In conclusion, Clostridium butyricum in the gut has anti-inflammatory effects on uterine tissues through alterations in the uterine microbiome and lipid metabolism. This study revealed a gut-uterus axis mechanism and provided insights into the treatment and prophylaxis of endometritis.

The effect of the female genital tract and gut microbiome on reproductive dysfunction

Microorganisms are ubiquitous in the human body; they are present in various areas including the gut, mouth, skin, respiratory tract, and reproductive tract. The interaction between the microbiome and reproductive health has become an increasingly compelling area of study. Disruption of the female genital tract microbiome can significantly impact the metabolism of amino acids, carbohydrates, and lipids, increasing susceptibility to reproductive tract diseases such as vaginitis, chronic endometritis, endometrial polyps, endometriosis, and polycystic ovary syndrome. The gut microbiome, considered an endocrine organ, plays a crucial role in the reproductive endocrine system by interacting with hormones like estrogen and androgens. Imbalances in the gut microbiome composition can lead to various diseases and conditions, including polycystic ovary syndrome, endometriosis, and cancer, although research on their mechanisms remains limited. This review highlights the latest advancements in understanding the female genital tract and gut microbiomes in gynecological diseases. It also explores the potential of microbial communities in the treatment of reproductive diseases. Future research should focus on identifying the molecular mechanisms underlying the association between the microbiome and reproductive diseases to develop new and effective strategies for disease prevention, diagnosis, and treatment related to female reproductive organs.

A Landscape View of the Female Genital Tract Microbiome in Healthy Controls and Women With Reproductive Health Conditions Associated With Ectopic Pregnancy

Disruption of the female genital microbiome is associated with several pregnancy complications, including miscarriage, preterm onset of labour, and tubal pregnancy. Ectopic pregnancy is a known cause of maternal morbidity and mortality, but early diagnosis and treatment of ectopic pregnancy remain a challenge. Despite growing established associations between genital microbiome and female reproductive health, few studies have specifically focused on its link with ectopic pregnancy. Therefore, the current review aims to provide a comprehensive account of the female genital microbiome in healthy and fertile women compared to those in ectopic pregnancy and its associated risk factors. The microbial diversity from various sites of the female genital tract was explored for a reliable proxy of female reproductive health in sequencing-based ectopic pregnancy research. Our report confirmed the predominance of Lactobacillus in the vagina and the cervix among healthy women. The relative abundance decreased in the vaginal and cervical microbiome in the disease state. In contrast, there were inconsistent findings on the uterine microbiome across studies. Additionally, we explore a spectrum of opportunities to enhance our understanding of the female genital tract microbiome and reproductive conditions. In conclusion, this study identifies gaps within the field and emphasises the need for visionary solutions in metagenomic tools for the early detection of ectopic pregnancy and other gynaecological diseases.

Clinical Relevance of Vaginal and Endometrial Microbiome Investigation in Women with Repeated Implantation Failure and Recurrent Pregnancy Loss

Recent studies have investigated if and how the vaginal and endometrial microbiome might affect endometrial receptivity and reproductive health. Although there is no consensus on the existence of a core uterine microbiome yet, evidence shows that the dominance of Lactobacillus spp. in the female reproductive tract is generally associated with eubiosis and improved chances of successful implantation and an ongoing pregnancy. Conversely, vaginal and endometrial dysbiosis can cause local inflammation and an increase of pro-inflammatory cytokines, compromising the integrity and receptivity of the endometrial mucosa and potentially hampering successful embryonic implantation. This review provides a critical appraisal of the influence of the vaginal and endometrial microbiome as parts of the female reproductive tract on fertility outcomes, focusing on repeated implantation failure (RIF) and recurrent pregnancy loss (RPL). It seems that RIF as well as RPL are both associated with an increase in microbiome diversity and a loss of Lactobacillus dominance in the lower female reproductive system.

Management strategies following implantation failure of euploid embryos

Background

Euploid blastocyst implantation failure may result from embryonic factors undetectable by preimplantation genetic testing for aneuploidy (PGT-A); however, various nonembryonic factors can also intricately interfere with implantation. This review seeks to clarify evidence-based testing and treatments for implantation failure after euploid embryo transfer.

Methods

We conducted a review of the literature on implantation failure after euploid embryo transfer or multiple embryo transfer cycles, which mainly included systematic reviews and meta-analyses.

Results

The recommended tests for implantation failure include (1) hysteroscopy, (2) endometrial CD138 immunohistochemistry and bacterial culture, (3) serum 25-hydroxyvitamin D3, and (4) thrombophilia screening. Based on diagnostic findings, the following treatments have been recommended: (1) antibiotics for chronic endometritis, (2) vitamin D replacement, (3) lifestyle modification, and (4) low-dose aspirin starting from the postimplantation period for thrombophilia. Moreover, frozen-thawed single euploid blastocyst transfer using assisted hatching and hyaluronan-enriched transfer medium may support embryo implantation.

Conclusion

To ensure a successful pregnancy in subsequent embryo transfers, simple, inexpensive, and evidence-based tests and treatments should be selected.

Current perspectives on endometrial receptivity: A comprehensive overview of etiology and treatment

Recurrent implantation failure (RIF) remains a challenging problem in assisted reproductive technology (ART). Further insights into uterine abnormalities that can disturb embryo implantation should be obtained. This review provides an overview of the effects of organic and non-organic uterine disorders on endometrial receptivity. The results suggest that various uterine pathologies can lead to defective embryo implantation via multiple mechanisms. In particular, uterine adenomyosis dysregulates molecular and cellular interactions that are vital for successful embryo implantation with a background of chronic inflammation, which may be alleviated by pretreatment with a gonadotropin-releasing hormone agonist. Uterine myomas can cause endometrial deformation and adverse alterations in uterine contractility. Nonetheless, the effectiveness of myomectomy remains debated, and endometrial polyp removal may be considered, particularly in patients with RIF. Chronic endometritis abrogates the appropriate uterine immunological environment critical for embryo implantation. Abnormal endometrial microbiota have been suggested to influence endometrial receptivity; however, supporting evidence is currently scarce. Platelet-rich plasma therapy may be a potential treatment for thin endometria; nevertheless, further validation is required. Endometrial receptivity analysis can detect dysregulation of the window of implantation, and new non-invasive methods for predicting endometrial receptivity have recently been proposed. However, numerous issues still need to be fully clarified. Further clinical and basic studies are necessary to investigate the pathophysiology of defective endometrial receptivity and identify optimal treatments for patients undergoing ART, especially those with RIF.

Culturomics in Unraveling the Upper Female Reproductive Tract Microbiota

In recent years, the study of the human microbiome has surged, shedding light on potential connections between microbiome composition and various diseases. One specific area of intense interest within this research is the female reproductive tract, as it holds the potential to influence the process of embryo implantation. Advanced sequencing technologies have delivered unprecedented insights into the microbial communities, also known as microbiota, residing in the female reproductive tract. However, their efficacy encounters significant challenges when analyzing low-biomass microbiota, such as those present in the endometrium. These molecular techniques are susceptible to contamination from laboratory reagents and extraction kits, leading to sequencing bias that can significantly alter the perceived taxonomy of a sample. Consequently, investigating the microbiota of the upper female reproductive tract necessitates the exploration of alternative methods. In this context, the current review delves into the application of culturomics in unraveling the upper female reproductive tract microbiota. While culturomics holds value in research, its transition to routine clinical practice appears remote, at least in the foreseeable future.

Uterine Microbiome: Does the Sampling Technique Matter?

Studies have proven the significance of microbial communities in various parts of the human body for health. In recent years it has been discovered that the uterine cavity is not sterile, and endometrium has its own microbiome which appears to have an impact on female fertility and gynecological pathologies. Lactobacillus has shown to dominate the microbial profile in the uterus and is considered an indicator of a healthy uterine environment. Yet, many argue that the Lactobacillus dominance is due to vaginal contamination during the sampling process. To date there is no clearly defined healthy endometrial microbial profile, which is largely due to the fact that determining the microbial community from the endometrium is complicated, and there is currently no consensus on sampling methods for the endometrial microbiome. As a result, this restricts ability to replicate discoveries made in other cohorts. Here we aim to give an overview of the sampling methods used and discuss what impedes the endometrial microbiome studies as well as how to reach a consensus on the study design. This knowledge could be incorporated into the future research and the knowledge on endometrial microbiome could be included into the diagnostics and treatment of female reproductive health.

Chronic Endometritis and Uterine Endometrium Microbiota in Recurrent Implantation Failure and Recurrent Pregnancy Loss

The aim of this study was to evaluate whether chronic endometritis (CE) and uterine endometrium microbiota were associated with repeated implantation failures (RIFs) and recurrent pregnancy losses (RPLs). In this prospective study, uterine endometrial specimens were obtained from 24 women with RIF, 27 with RPL, and 29 fertile control women. Immunohistochemical staining of CD138 for CE and 16S ribosomal RNA (rRNA) sequencing analysis for uterine endometrium microbiota were performed simultaneously. To assess CE, Liu's method, McQueen scores and plasma cell count/10 mm2 were used. The frequency of CE (plasma cells > 5.15/10 mm2) was higher in women with RPL (29.6%) than in fertile controls (6.8%, p < 0.05). The plasma cell count/10 mm2 in women with RPL (median 1.53, range 0-252.6, p < 0.01) and women with RIF (median 0.6, range 0-6.98, p < 0.05) was higher than in fertile controls (median 0, range 0-29). The uterine endometrium microbiota in women with RPL or RIF was not significantly different from that in fertile controls. However, the relative dominance rate of Lactobacillus iners (median 4.7%, range 0-99.9 vs. median 0%, range 0-100, p < 0.001) and the positive rate of Ureaplasma species (36.3% vs. 8.6%, p < 0.05) were higher in 11 women with CE than in 69 women without CE. The results suggest that CE may be involved in the pathophysiology of RPL and RIF. Lactobacillus iners and Ureaplasma species may be associated with the etiology of CE.

The Endometrial Microbiota: Challenges and Prospects

Contrary to popular belief, we have known for many years that the endometrium is not a sterile environment and is considered to be a low-biomass milieu compared to the vagina. Numerous trials and studies have attempted to establish a valid sampling method and assess its physiological composition, but no consensus has been reached. Many factors, such as ethnicity, age and inflammation, can influence the microbiome. Moreover, it possesses a higher alpha-diversity and, therefore, contains more diverse bacteria than the vagina. For instance, Lactobacillus has been shown to be a predominant genus in the vaginal microbiome of healthy women. Consequently, even if a majority of scientists postulate that a predominance of Lactobacillus inside the uterus improves reproductive outcomes, vaginal contamination by these bacteria during sampling cannot be ruled out. Certain pathologies, such as chronic endometritis, have been identified as inflammation perpetrators that hinder the embryo implantation process. This pro-inflammatory climate created by dysbiosis of the endometrial microbiota could induce secondary inflammatory mediators via Toll-like receptors, creating an environment conducive to the development of endometriosis and even promoting carcinogenesis. However, studies to this day have focused on small populations. In addition, there is no clearly defined healthy uterine composition yet. At most, only a few taxa have been identified as pathogenic. As sampling and analysis methods become increasingly precise, we can expect the endometrial microbiota to be incorporated into future diagnostic tools and treatments for women's health.

A Narrative Review Discussing the Obstetric Repercussions Due to Alterations of Personalized Bacterial Sites Developed within the Vagina, Cervix, and Endometrium

BACKGROUND

The reproductive tract microbiota that evolved as an integrative component has been studied intensively in the last decade. As a result, novel research, clinical opportunities, and perspectives have been derived following the close investigation of this microecological environment. This has paved the way for an update to and improvement of the management strategies and therapeutic approaches. However, obscurities, contradictions, and controversies arise regarding the ascension route from the vagina to the endometrium via the cervix, with finality in adverse obstetric outcomes.

METHODS

Starting from these considerations, we aimed to gather all existing data and information from four major academic databases (PubMed, ISI Web of Knowledge, Scopus, and ScienceDirect) published in the last 13 years (2010-2023) using a controlled vocabulary and dedicated terminology to enhance the coverage, identification, and sorting of potentially eligible studies.

RESULTS

Despite the high number of returned entries (n = 804), only a slight percentage (2.73%) of all manuscripts were deemed eligible following two rounds of evaluation. Cumulatively, a low level of Lactobacillus spp. and of other core microbiota members is mandatory, with a possible eubiosis-to-dysbiosis transition leading to an impairment of metabolic and endocrine network homeostasis. This transposes into a change in the pro-inflammatory landscape and activation of signaling pathways due to activity exerted by the bacterial lipopolysaccharides (LPSs)/endotoxins that further reflect a high risk of miscarriage in various stages. While the presence of some pathogenic entities may be suggestive of an adverse obstetric predisposition, there are still pros and cons of the role of specific strains, as only the vagina and cervix have been targeted as opposed to the endometrium, which recently started to be viewed as the key player in the vagina-cervix-endometrium route. Consequently, based on an individual's profile, diet, and regime, antibiotics and probiotics might be practical or not.

CONCLUSIONS

Resident bacteria have a dual facet and are beneficial for women's health, but, at the same time, relaying on the abundance, richness, and evenness that are definitory indexes standing as intermediaries of a miscarriage.

Pregnancy outcomes after vaginal probiotic supplementation before frozen embryo transfer: a randomized controlled study

In women receiving assisted reproductive treatment, intrauterine lactobacilli dominance has been associated with higher rates of pregnancy achievement. This randomized controlled trial conducted in the fertility clinic of the university hospital from 7 August 2019 to May 2021, aimed to compare the clinical outcome of embryo transfer in frozen-thaw cycles with Lactobacillus supplementation prior to embryo transfer and the standard treatment. A total of 340 infertile women underwent randomization. The biochemical and clinical pregnancy rates were comparable between the groups (39.9 and 34.2% in the study group vs. 41.8 and 31.7% in the control group); however, the miscarriage rate was significantly decreased in the study group (9.5 vs. 19.1%, respectively, p = 0.02), [OR = 0.44, 95% CI (0.23, 0.86)]. Among 49 women diagnosed with bacterial vaginosis, the live birth rate in the study group was higher than the control group (42.31 vs. 26.09%, p = 0.23), [OR = 2.08, 95% CI (0.62, 6.99)]. In the blastocyst transfer group (n = 206), the live birth rate was significantly higher in the study group than in the control group (35.71 vs. 22.22%, p = 0.03) [OR = 1.9, 95% CI (1.05, 3.59)]. Therefore, intravaginal lactobacilli supplementation before embryo transfer in the frozen-thaw cycle did not improve the biochemical and clinical pregnancy rate in the general population but significantly reduced the miscarriage rate.Trial Registration: TCTR20190429001 (29/04/2019) @ www.thaiclinicaltrials.org .

Metataxonomic Analysis of the Uterine Microbiota Associated with Low Fertility in Dairy Cows Using Endometrial Tissues Prior to First Artificial Insemination

The deterioration in reproductive performance in association with low fertility leads to significant economic losses on dairy farms. The uterine microbiota has begun to attract attention as a possible cause of unexplained low fertility. We analyzed the uterine microbiota associated with fertility by 16S rRNA gene amplicon sequencing in dairy cows. First, the alpha (Chao1 and Shannon) and beta (unweighted and weighted UniFrac) diversities of 69 cows at four dairy farms that had passed the voluntary waiting period before the first artificial insemination (AI) were analyzed with respect to factors including farm, housing style, feeding management, parity, and AI frequency to conception. Significant differences were observed in the farm, housing style, and feeding management, except parity and AI frequency to conception. The other diversity metrics did not show significant differences in the tested factors. Similar results were obtained for the predicted functional profile. Next, the microbial diversity analysis of 31 cows at a single farm using weighted UniFrac distance matrices revealed a correlation with AI frequency to conception but not with parity. In correlation with AI frequency to conception, the predicted function profile appeared to be slightly modified and a single bacterial taxon, Arcobacter, was detected. The bacterial associations related to fertility were estimated. Considering these, the uterine microbiota in dairy cows can be varied depending on the farm management practices and may become one of the measures for low fertility. IMPORTANCE We examined the uterine microbiota associated with low fertility in dairy cows derived from four commercial farms via a metataxonomic approach using endometrial tissues prior to the first artificial insemination. The present study provided two new insights into the relevance of uterine microbiota with respect to fertility. First, the uterine microbiota varied depending on housing style and feeding management. Next, a subtle change was observed in functional profile analysis: a formation of uterine microbiota was detected to be different in correlation with fertility in one farm studied. Considering these insights, an examination system on bovine uterine microbiota is hopefully established based on continuous research on this topic.

Vaginal and Cervical Microbiota Composition in Patients with Endometrial Cancer

According to recent data, changes in the vaginal microbiota could affect the risk of gynaecological cancers. Women suffering from endometrial cancer present significant changes in cervicovaginal microbiota composition. The objective of our study was to characterize the cervicovaginal microbiota of women undergoing hysterectomy due to benign disease, atypical hyperplasia, and endometrial cancer; The study included 96 patients, who undergone surgical treatment due to benign uterine disease, precancerous endometrial lesion, and endometrial cancer. Quantitative and qualitative real-time PCR analysis of DNA isolated from vaginal fornix and endocervical canal samples was performed to detect the 19 most commonly identified microorganisms, including different Lactobacillus spp., Atopobium, Bifidobacterium, Chlamydia, and Gardnerella; At least one of the tested microorganisms was identified in 88.5% of vaginal and 83.3% of cervical samples. Lactobacillus iners was significantly more frequent in patients with benign condition, whereas Dialister pneumosintes and Mobiluncus curtisii was more frequent in cancer patients; Mobiluncus curtisi and Dialister pneumosintes, which were identified as significantly more common in endometrial cancer vaginal samples, may be considered as potential endometrial cancer co-factors which promote/stimulate carcinogenesis. However, the exact mechanism of such activity remains unexplained and requires further investigations.

Comparison of microbial profiles and viral status along the vagina-cervix-endometrium continuum of infertile patients

For decades, the endometrium was considered to be a sterile environment. However, now this concept is disputed, and there is growing evidence that microbiota composition might affect endometrial receptivity. Routine clinical management of infertility is still limited to a microbiological assessment of the lower reproductive tract. The purpose of this study was to compare the abundance of various bacterial, fungal, and viral species, qualitatively and quantitatively, in vaginal, cervical, and endometrial biomaterial of infertile patients. A total of 300 samples from 100 infertile patients of a private assisted reproduction clinic were analyzed. A broad real-time polymerase chain reaction panel was used to identify 28 relevant microbial taxa as well as three members of the Herpesviridae family. All patients underwent endometrial biopsy for further histopathological evaluation. Analysis of the microbial diversity (within the boundaries of the detection panel) revealed that Shannon indexes in the cervix and vagina were similar (1.4 × 10^-2 (1.6 × 10^-3 - 6.5 × 10^-1) vs 1.9 × 10^-2 (2.3 × 10^-3 - 5.3 × 10^-1), respectively, p = 0.502), whereas endometrial indexes differed significantly from both regions (0 (0 - 1.4 × 10^-1), p < 0.0001). Surprisingly, 17 microbial and viral taxa were detected in at least one sample. Endometrium exhibited a quite distinct microbiological profile, being different at the detection rates of 14 taxa (p < 0.05). Remarkably, 4% and 2% of endometrial samples were positive for Cytomegalovirus and Candida spp., respectively, while these were undetectable in corresponding cervical and vaginal samples. Prevalence of the Gardnerella vaginalis + Prevotella bivia + Porphyromonas spp. group in endometrium was associated with a low abundance of Lactobacillus spp. (p = 0.039). No noteworthy associations were identified between various microbiota characteristics and clinical parameters, such as chronic endometritis, uterine polyps and adhesions, endometriosis, and a history of sexually transmitted infections. These findings indicate that the microbiological profile of the endometrium is unique, and the analysis of the lower reproductive tract should supplement, rather than be a substitute for it.

Chronic endometritis increases the recurrence of endometrial polyps in premenopausal women after hysteroscopic polypectomy

BACKGROUND

The reported recurrence rate of endometrial polyps (EPs) after hysteroscopic polypectomy varied widely, and the factors influencing the recurrence of EPs are still controversial. Furthermore, the known definite independent risk factors are almost unchangeable, such as the number of EPs and previous polypectomy history. The aim of this study was to evaluate the impact of chronic endometritis (CE) on the recurrence of EPs in premenopausal women who underwent hysteroscopic polypectomy.

METHODS

A retrospective study was conducted at a university-affiliated hospital. Premenopausal women who underwent hysteroscopic polypectomy were enrolled, and those with definite confounding factors for polyp recurrence were excluded, including endometriosis and previous polypectomy history. A total of 233 women were enrolled in this study, including 64 (27.5%) cases with CE and 169 (72.5%) cases without CE. CE was diagnosed via immunohistochemical detection of CD138 on the endometrial specimen. Comparison of the recurrence rate of EPs was performed in women with or without CE at each monitoring stage (i.e., at 3, 6, 9 and 12 months) after hysteroscopic polypectomy.

RESULTS

The recurrence rates of EPs at one year in patients with and without CE were 26.6% (95% confidence interval [CI] 15.8-37.4%) and 9.5% (95% CI 5.0-14.0%), respectively, with an overall recurrence rate of 14.2% (95% CI 9.7-18.7%). The hazard ratio (HR) for EPs recurrence in the EPs with CE cohort versus the EPs without CE cohort was 3.08 (95% CI 1.56-6.09) (P = 0.001). Similarly, the recurrence rate of EPs was significantly higher in women with CE than in those without CE at each monitoring stage (i.e., 3, 6 and 9 months). CE and multiple EPs were risk factors for EPs recurrence. The HR for EPs recurrence in the EPs with CE cohort compared with the EPs without CE cohort was 3.06, after adjustment for the number of EPs.

CONCLUSIONS

CE was a harmful factor for the recurrence of EPs in premenopausal women after hysteroscopic polypectomy. Thus, routine screening for CE during hysteroscopic polypectomy was needed. Frequent monitoring was needed for multiple EPs as the number of EPs also contributed to polyp recurrence.

Analysis of pregnancy outcomes in patients with recurrent implantation failure complicated with chronic endometritis

Chronic endometritis (CE) has been considered to reduce uterine receptivity and negatively affect reproductive outcomes for in vitro fertilization-embryo transfer (IVF-ET) patients, especially for people undergoing recurrent implantation failure (RIF). To investigate the effects of antibiotic and platelet-rich plasma (PRP) therapy on pregnancy outcomes following frozen-thawed embryo transfer (FET) in RIF patients with CE, endometrial specimens of 327 patients with RIF obtained by endometrial scratching during mid-luteal phase were immunostained by multiple myeloma oncogene-1 (Mum-1)/syndecan-1 (CD138). RIF patients with CE were given antibiotics and PRP treatment. According to the Mum-1⁺/CD138⁺ plasmacytes after treatment, patients were divided into persistent weak positive CE (+) group, CE (-) group and non-CE group. FET was performed and the basic characteristics and pregnancy outcomes of patients in three groups were compared. Among 327 RIF patients, 117 patients were complicated with CE, the prevalence was 35.78%. The prevalence of strong positive was 27.22% and that of weak positive was 8.56%. 70.94% patients with CE converted to negative after treatment. There was no significant difference in the basic characteristics, including age, BMI, AMH, AFC, infertility years, infertility types, number of previous transplant cycles, endometrial thickness on transplantation day and number of transplanted embryos (p > 0.05); The positive rate of hCG, clinical pregnancy rate and implantation rate in CE (-) group were significantly increased compared with the weak CE (+) group and non-CE group (p < .01), and the live birth rate also improved (p < .05). Whereas, the rate of early abortion in CE (-) group was 12.70%, which was higher than that in weak CE (+) group and non-CE group (p < .05). After multivariate analysis, number of previous failed cycles and CE remained independent factors associated with live birth rate, while only CE remained to be the independent factor of clinical pregnancy rate. It is recommended to perform CE-related examination for patients with RIF. Antibiotic and PRP treatment can significantly improve pregnancy outcomes of patients with CE negative conversion in FET cycle.

Commonalities and Disparities between Endometriosis and Chronic Endometritis: Therapeutic Potential of Novel Antibiotic Treatment Strategy against Ectopic Endometrium

Chronic endometritis (CE) is a local mucosal inflammatory disorder of the uterine lining, which is histopathologically recognized as the unusual infiltration of CD138(+) plasmacytes into the endometrial stromal compartment. Accumulating body of research documented that CE is associated with female infertility and several obstetric/neonatal complications. The major cause of CE is thought to be intrauterine infection represented by common bacteria (Escherichia coli, Enterococcus faecalis, Streptococcus, and Staphylococcus), Mycoplasma/Ureaplasma, and Mycobacterium. Additionally, local dysbiosis in the female reproductive tract may be involved in the onset and development of CE. Antibiotic treatments against these microorganisms are effective in the elimination of endometrial stromal plasmacytes in the affected patients. Meanwhile, endometriosis is a common female reproductive tract disease characterized by endometriotic tissues (ectopic endometrium) growing outside the uterus and potentially causes chronic pelvic symptoms (dysmenorrhea, dyspareunia, dyschezia, and dysuria), infertility, and ovarian cancers. Endometriosis involves endocrinological, genetic, and epigenetic factors in its etiology and pathogenesis. Recent studies focus on immunological, inflammatory, and infectious aspects of endometriosis and demonstrate several common characteristics between endometriosis and CE. This review aimed to better understand the immunological and microbial backgrounds underlying endometriosis and CE and look into the therapeutic potential of the novel antibiotic treatment strategy against endometriosis in light of endometrial infectious disease.

The alteration of intrauterine microbiota in chronic endometritis patients based on 16S rRNA sequencing analysis

BACKGROUND

Chronic endometritis (CE) is a disease of continuous and subtle inflammation occurring in the endometrial stromal area, which is often asymptomatic or present with non-specific clinical symptoms.

METHODS

This study investigated the composition and distribution of the intrauterine microbiota of 71 patients who underwent hysteroscopy during the routine clinical inspection of infertility. Among them, patients who were diagnosed with chronic endometritis (CE) were allocated into CE group (n = 29) and others into non-CE group (n = 42). There was no significant difference in average age between the two groups (P = 0.19). Uterine flushing fluid was collected by the self-developed cervical trocar uterine cavity sampler and 16S rRNA sequencing was performed.

RESULTS

The alpha diversity in the CE group was significantly higher than that in the non-CE group (P < 0.05). Firmicutes (newly named Bacillota) were the dominant phylum in the non-CE group (72.23%), while their abundance was much lower in the CE group (49.92%), but there was no statistically significant difference between the two groups. The abundances of Actinobacteriota and Cyanobacteria in the CE group were significantly higher than those in the non-CE group (P < 0.05). At the genus level, the abundance of Lactobacillus dominated in all samples, which presented a significantly lower abundance in the CE group (40.88%) than that in the non-CE group (64.22%) (P < 0.05). Correspondingly, the abundance of non-Lactobacillus was higher in the CE group, among which Pseudomonas and Cutibacterium increased significantly (P < 0.01). Moreover, compared with the non-CE group, the pathways involved in arginine and proline metabolism and retinol metabolism were significantly enriched in the CE group (P < 0.05), while the metabolism of lipid and prenyltransferases were significantly decreased in the CE group (P < 0.05).

CONCLUSIONS

A certain microbial community was colonized in the uterine cavity, which was dominated by Lactobacillus. The structure and distribution of intrauterine microbiota in the CE group were different from those in the non-CE group by showing a lower abundance of Lactobacillus, and a significantly higher abundance of Pseudomonas and Cutibacterium. Additionally, the microbial metabolism was altered in the CE group. This study elaborated the alteration of intrauterine microbiota in CE patients, which may contribute to the diagnosis of CE and provide a reference for antibiotic treatment of CE.

Therapeutic efficacy of gentle endometrial curettage on antibiotic-resistant chronic endometritis in infertile women

Purpose

To identify the efficacy of endometrial curettage on antibiotic-resistant chronic endometritis (CE) in infertile women.

Methods

Of 1580 women with CE, 87 with antibiotic-resistant CE after two to five cycles of antibiotic treatment were recruited between 2019 and 2021. The women who underwent endometrial curettage without applying any force and, in the subsequent menstrual cycle, endometrial sampling for CD138 immunostaining without antibiotic use. Pregnancy outcomes after in vitro fertilization treatment were analyzed in women who did not desire endometrial curettage and in those with cured and persistent CE after endometrial curettage.

Results

In 64 women who underwent endometrial curettage, the number of CD138-positive cells decreased from 28.0 ± 35.3 to 7.7 ± 14.0 (p < 0.0001), and CE in 41 women (64.1%) was cured (<5 CD138-positive cells). The pathological findings detected 3.1% of endometrial hyperplasia and 1.6% of endometrial cancer. The ongoing pregnancy rates in women aged ≤42 without endometrial curettage were significantly lower than those of women with cured and persistent CE (26.7%, 67.6%, and 57.1%, respectively, p = 0.03).

Conclusions

Gentle endometrial curettage for antibiotic-resistant CE significantly decreased the number of CD138-positive cells, resulting in improved pregnancy outcomes regardless of remaining CE. Endometrial curettage is also important as a screening for endometrial malignancy.

Therapeutic intervention based on gene sequencing analysis of microbial 16S ribosomal RNA of the intrauterine microbiome improves pregnancy outcomes in IVF patients: a prospective cohort study

PURPOSE

A Lactobacillus-dominated microbiota in the endometrium was reported to be associated with favorable reproductive outcomes. We investigated in this study whether 16S ribosomal RNA (rRNA) gene sequencing analysis of the uterine microbiome improves pregnancy outcomes.

METHODS

This prospective cohort study recruited a total of 195 women with recurrent implantation failure (RIF) between March 2019 and April 2021 in our fertility center. Analysis of the endometrial microbiota by 16S rRNA gene sequencing was suggested for all patients who had three or more failed embryo transfers (ETs). One hundred and thirty-one patients underwent microbial 16S rRNA gene sequencing (study group) before additional transfers, while 64 patients proceeded to ET without that analysis (control group). The primary outcome was to compare the cumulative clinical pregnancy rate of two additional ETs.

MAIN RESULTS

An endometrial microbiota considered abnormal was detected in 30 patients (22.9%). All but one of these 30 patients received antibiotics according to the bacterial genus detected in their sample, followed by treatment with probiotics. As a result, the cumulative clinical pregnancy rate (study group: 64.5% vs. control group: 33.3%, p = 0.005) and the ongoing pregnancy rate (study group: 48.9% vs. control group: 32.8%, p = 0.028) were significantly increased in the study group compared to the control group.

CONCLUSION

Personalized treatment recommendations based on the microbial 16S rRNA gene sequencing of the uterine microbiota can improve IVF outcomes of patients with RIF.

TRIAL REGISTRATION

The University Hospital Medical Information Network (UMIN) Clinical Trial Registry: UMIN000036050 (date of registration: March 1, 2019).

Gut and genital tract microbiomes: Dysbiosis and link to gynecological disorders

Every year, millions of women are affected by genital tract disorders, such as bacterial vaginosis (BV), endometrial cancer, polycystic ovary syndrome (PCOS), endometriosis, and uterine fibroids (UFs). These disorders pose a significant economic burden on healthcare systems and have serious implications for health and fertility outcomes. This review explores the relationships between gut, vaginal, and uterine dysbiosis and the pathogenesis of various diseases of the female genital tract. In recent years, reproductive health clinicians and scientists have focused on the microbiome to investigate its role in the pathogenesis and prevention of such diseases. Recent studies of the gut, vaginal, and uterine microbiomes have identified patterns in bacterial composition and changes across individuals' lives associated with specific healthy and diseased states, particularly regarding the effects of the estrogen-gut microbiome axis on estrogen-driven disorders (such as endometrial cancer, endometriosis, and UFs) and disorders associated with estrogen deficiency (such as PCOS). Furthermore, this review discusses the contribution of vitamin D deficiency to gut dysbiosis and altered estrogen metabolism as well as how these changes play key roles in the pathogenesis of UFs. More research on the microbiome influences on reproductive health and fertility is vital.