Endometriosis, a chronic disease that affects about 10% of women of reproductive age, is characterized by severe pain and growth of endometrium-like tissues outside the uteri. Although several theories have been advanced for the cause of endometriosis, no theory fully explains why endometriosis occurs. For this study, we strove to elucidate a new mechanism of endometriosis leading to establishment of a new therapeutic strategy for its treatment. In our murine endometriosis model, a marked hypoxic state was induced in the peritoneal cavity, as indicated by increased expression of HIF-1α in peritoneal exudate cells. Moreover, innate immune response, such as TLR4 and IL-1β expression, was upregulated. To restore the hypoxic milieu in endometriosis, we chose resveratrol (RSV), a natural polyphenolic compound, as a hypoxia-reducing agent. As expected, RSV administration decreased the number of HIF-1α-positive cells. Furthermore, RSV administration reduced the size and weight of endometriotic lesions significantly. However, RSV administration did not change TLR4 and IL-1β expression levels in peritoneal exudate cells. In the process of seeking mechanisms of endometriosis other than TLR4-dependent and IL-1β-dependent pathways, we detected autoantibody deposition in endometriotic lesions. In endometriotic lesions from RSV-administered mice, accumulation of autoantibodies was inhibited compared to a control group. As described herein, we proposed a new concept by which autoantibody deposition can cause endometriosis, raising the possibility of RSV as a promising therapeutic option for endometriosis.

The magnetic resonance imaging (MRI)-based classification of adenomyosis subtypes helps predict reproductive and obstetric outcomes; however, background factors associated with use of assisted reproductive technology (ART) and live birth within each individual subtype remain unclear. We conducted a multicenter retrospective study of 199 premenopausal women (32–49 years) who underwent pelvic MRI and laparoscopic surgery and had histopathologic confirmation of adenomyosis (January 2010–May 2023). Patients were classified as intrinsic (n = 58), extrinsic (n = 61), or indeterminate (n = 80) subtype. Within each subtype, multivariate logistic regression tested independent associations of age, ART history, gravidity, parity, lesion thickness, and intraoperative findings—including pelvic endometriosis—with ART use and live birth. The extrinsic subtype had a higher proportion with ART history than the intrinsic subtype (32.8

Background:Relugolix, an oral gonadotropin-releasing hormone (GnRH) antagonist, represents a potentially effective and less invasive therapeutic approach for retained products of conception (RPOC). However, its impact on subsequent pregnancy outcomes remains unclear. This study aimed to evaluate these outcomes following GnRH antagonist treatment for RPOC. Methods:This single-center cohort study encompassed 20 patients diagnosed with RPOC following miscarriage or abortion before 22 gestational weeks who were treated with oral relugolix, a GnRH antagonist, from January 2022 to July 2024. Following treatment completion and hysteroscopic confirmation of complete resolution, 12 patients subsequently conceived and were prospectively followed for pregnancy and neonatal outcomes. To contextualize outcomes, results were compared with the non-GnRH antagonist group managed at the same institution from 2014 to 2021 without GnRH antagonist exposure. Results:The GnRH antagonist group had fewer patients requiring surgical intervention than the non-GnRH antagonist group [30.0% (6/20) vs. 70.1% (54/77), p = 0.002], underscoring the reduced invasiveness of medical therapy. Of the 12 pregnancies following relugolix treatment, 4 led to early miscarriage and 8 progressed beyond 22 gestational weeks. The GnRH antagonist and non-GnRH antagonist groups exhibited comparable clinical pregnancy and live birth rates (53.3% vs. 73.3 and 33.3% vs. 48.9% per embryo transfer, respectively; not significant). Similarly, the interval from RPOC diagnosis in the previous pregnancy to gestational sac confirmation in the current pregnancy (328.9 ± 153.4 vs. 486.9 ± 658.8 days) and the interval from RPOC treatment completion to gestational sac confirmation (295.7 ± 166.6 vs. 445.8 ± 628.2 days) did not significantly differ between both groups. Conclusion:Relugolix therapy for RPOC was associated with preserved fertility and favorable pregnancy outcomes comparable to conventional management.

PURPOSE:Although studies have suggested a link between gut microbiota and endometriosis pathophysiology, the effects of treatment for endometriosis remain unclear. METHODS:In this prospective observational study, 27 patients with stage III/IV endometriosis and 17 healthy controls provided a total of 56 fecal samples. In endometriosis patients, gut microbiota profiles were analyzed before and after hormonal therapy or surgery to assess treatment-related changes. 16S rRNA gene sequencing was used for microbiota analysis. RESULTS:No differences in α- or β-diversity were observed between the endometriosis and control groups, although patients with endometriosis had high levels of Acidaminococcus, Lachnoclostridium, and Paraprevotella and low levels of Odoribacter (all p < 0.05). Among the eight patients who received hormonal therapy, no significant changes in α- and β-diversity were observed between the pre- and post-treatment samples. A comparison of samples from the same individuals showed an increase in Blautia, which is associated with mental health stability, and a decrease in Sutterella, which is involved in regulating the intestinal barrier. In an exploratory analysis of patients without recurrence after surgery (n = 4), α-diversity significantly increased (p = 0.035), with stable β-diversity. Postsurgical increases were observed in 10 genera, including six inflammation-related taxa; five (Flavonifractor, [Eubacterium]_brachy_group, Hungatella, Incertae_Sedis, and Fournierella) are associated with anti-inflammatory effects. CONCLUSIONS:Hormonal therapy for endometriosis may help not only to control lesions but also to support mental health. Surgical treatment may alter the composition of inflammation-associated gut bacteria; however, these exploratory results from a small cohort should be interpreted with caution. Further studies with larger sample sizes are warranted.

INTRODUCTION:Retained products of conception (RPOC) may necessitate invasive interventions, such as uterine artery embolization (UAE). Hysteroscopic surgery with a balloon catheter (BC) in the internal iliac artery may reduce the risk of fertility loss. However, its therapeutic efficacy and subsequent pregnancy outcome have not been studied. MATERIAL AND METHODS:With Ethics Committee approval and informed patient consent, we enrolled seven cases of RPOC managed with hysteroscopic surgery using a BC (BC group) between January 2019 and September 2023. These cases were retrospectively compared in terms of the treatment course and postoperative reproductive outcomes in 12 patients who underwent hysteroscopic procedures with UAE (UAE group). RESULTS:No differences were observed between the BC and UAE groups in patient demographics, operative time, and intraoperative blood loss. The median hospital stay was significantly shorter in the BC group (p < 0.05). In the UAE group, there was a higher percentage of patients with a fever above 38 °C on postoperative day 1 (p < 0.044). The interval from RPOC diagnosis to interventional radiology was comparable between the groups (median [range]; BC:15 [1-29] vs UAE: 13 [1-25] days), as was the interval from IVR to subsequent pregnancy (325.5 [123-925] vs 312 [78-2253] days). After surgery, five women in the BC group experienced 8 pregnancies, of which two resulted in spontaneous abortion and six in live births. No differences were found in the rate of obstetric complications between the two groups. CONCLUSION:Hysteroscopic surgery with BC demonstrated comparable safety to hysteroscopic surgery with UAE. Compared with UAE, hysteroscopic surgery with BC may shorten hospital stay and contribute to fertility preservation by transiently obstructing uterine blood perfusion.

OBJECTIVE:To investigate whether intraoperative confirmation of the disappearance of uterine cavity blood flow using color Doppler during manual vacuum aspiration (MVA) for missed miscarriage reduces the occurrence of retained products of conception (RPOC). METHODS:We conducted a retrospective cohort study of 202 patients who underwent MVA for missed miscarriage before 12 weeks of gestation at the University of Yamanashi between April 2019 and July 2025. Patients were divided into a flow-confirmation group, in which intraoperative transvaginal ultrasound with color Doppler was used to confirm the disappearance of blood flow, and a non-confirmation group. The primary outcome was the occurrence of RPOC diagnosed by postoperative ultrasound. Patient characteristics and surgical variables were compared between groups. RESULTS:RPOC occurred in 25 of 202 cases (12%). None of the 25 patients in the flow-confirmation group developed RPOC, whereas 14% of the 177 patients in the non-confirmation group did (P = 0.04). The surgeon's years of experience (2.6 ± 1.6 vs 4.9 ± 4.7 years, P = 0.004) and postoperative follow-up duration (1.9 ± 1.0 vs 3.3 ± 4.3 weeks, P = 0.02) were significantly shorter in the flow-confirmation group, but no other significant differences were found in baseline characteristics or surgical variables. CONCLUSION:Intraoperative confirmation of the disappearance of uterine cavity blood flow using color Doppler during MVA is a simple, safe, and effective technique to prevent RPOC. This approach may reduce the need for repeat surgery and postoperative hemorrhage and could be incorporated into standard MVA protocols.

Background:Anti-β2GPI/HLA-DR autoantibodies may be involved in recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL). We examined their association with the endometrial microbiome and chronic endometritis (CE). Methods:In this cross-sectional study, 141 women (54 RIF, 87 RPL) were enrolled. Serum anti-β2GPI/HLA-DR positivity was defined using 99th/95th percentile cut-offs. Endometrial microbiome was assessed by 16S rRNA sequencing, focusing on reproductive-failure-related species (Gardnerella, Prevotella, Atopobium, Dialister, Anaerococcus, Ureaplasma, Mycoplasma). Microbiome and CE were compared by antibody status in RIF and RPL. Results:In RIF, antibody-positive women more frequently had Lactobacillus iners (99‰ and 95‰ cut-offs: 71.4% vs. 23.4%, p = 0.03; and 70.0% vs. 20.5%, p = 0.026) and reproductive-failure-related bacterial species (99‰: 100% vs. 51.1%, p = 0.016; 95‰: 90.0% vs. 52.3%, p = 0.032). In multivariable analysis with 95‰ cut-off, Lactobacillus iners (OR 13.1, p = 0.003) and reproductive-failure-related species (OR 9.64, p = 0.029) were independently associated with antibody positivity. In RPL, Anaerococcus was more frequent in antibody-positive women. CE frequency did not differ by antibody status in RIF or RPL. Conclusion:Anti-β2GPI/HLA-DR antibody positivity was associated with endometrial dysbiosis and may serve as a biomarker of abnormal intrauterine environment in reproductive failure.

BACKGROUND:To investigate the association between menstrual-related disorders and sexually transmitted infections (STI) among young women in Japan, and to examine differences according to disorder type and hormonal therapy use. METHODS:This cross-sectional study used the Japan Medical Data Center Claims Database and included women younger than 40 years who had at least one healthcare visit in 2023. Menstrual-related disorders were defined as endometriosis or dysmenorrhea based on ICD-10 codes. The prevalence of five STIs-gonorrhea, genital chlamydia infection, trichomoniasis, genital herpes, and other sexually transmitted conditions-was compared between women with and without menstrual-related disorders. Subgroup analyses were conducted for endometriosis, dysmenorrhea, and hormonal therapy (low-dose estrogen-progestin combinations or dienogest). Prevalence ratios (PR) and prevalence differences (PD) with 95% confidence intervals (CI) were estimated. RESULTS:Among 3,440,929 women, 257,897 (7.5%) had menstrual-related disorders. All STI were substantially more prevalent in this group than in women without menstrual-related disorders, with PRs ranging from 4.31 to 5.29. Endometriosis showed the highest prevalence, particularly for genital chlamydia infection (4.98%; PR 7.44). Dysmenorrhea was also associated with consistently elevated STI prevalence. Among women with menstrual-related disorders, STI prevalence differed only slightly according to hormonal therapy use, with differences generally within one percentage point. CONCLUSION:Menstrual-related disorders were strongly associated with increased diagnosis of STI in Japanese young women. These findings highlight the importance of integrating STI screening and reproductive health education into routine gynecologic care for women with endometriosis or dysmenorrhea. The influence of healthcare-seeking behavior and diagnostic patterns should be considered when interpreting claims-based STI data.

Anti-β2GPI/HLA-DR antibody, chronic endometritis (CE), and endometrial dysbiosis are likely to be associated with the etiologies of recurrent pregnancy loss (RPL). This prospective cohort study aimed to investigate these new risk factors together with conventional causes for RPL, and to evaluate pregnancy outcomes in women individually treated. A total of 87 women with RPL underwent conventional assessment together with anti-β2GPI/HLA-DR antibody measurements, CD138 immunohistochemistry for CE, and 16S rRNA sequence analysis for endometrial microbiome. Women with anti-β2GPI/HLA-DR antibody, CE, and endometrial dysbiosis received low-dose aspirin and heparin, antibiotics, and probiotics, respectively. Pregnancy outcomes of the participants were assessed. Anti-β2GPI/HLA-DR antibody, CE, non-Lactobacillus-dominant microbiome (NLDM)-1 (Lactobacillus + Bifidobacterium < 80%), and NLDM-2 (Lactobacillus without iners + Bifidobacterium < 80%) were detected in 16 (18.4%), 22 (25.3%), 27 (31.0%), and 46 (52.8%) women, respectively. Based on conventional assessment, 65.5% of women with RPL were classified as unexplained etiology; however, the percentage reduced to 16.1% when these new tests were assessed together. All 9 pregnancies with anti-β2GPI/HLA-DR antibody, 13 (92.9%) of 14 pregnancies with CE, and 24 (92.3%) of 26 pregnancies with NLDM-2 resulted in live birth. Assessment of these new tests may be clinically useful for reducing the proportion of unexplained RPL, and for providing high live birth rates if women receive relevant treatments.

Abstract Background Macrophages are essential immune cells critical to reproductive physiology. They regulate key processes such as follicular development, ovulation, and luteinization in the ovaries. Macrophages are also involved in endometrial remodeling, immune tolerance, and placentation in the uterus. Methods This review examined the biological characteristics of macrophages and their role in ovarian, uterine, and fallopian tube physiology. It focused on findings from both animal and human studies to provide a comprehensive understanding of macrophage functions. Main Findings In the ovaries, M1 macrophages play a role in folliculogenesis and ovulation through the inflammatory and angiogenic pathways. Macrophages also maintain the corpus luteum and vascular integrity. In the uterus, macrophages regulate tissue repair and remodeling during the menstrual cycle and play a critical role in implantation by maintaining immune tolerance and supporting decidualization. Dysregulation of the M1/M2 balance can cause implantation failure. In the fallopian tubes, macrophages mediate tissue repair and immune responses. Macrophage polarization dynamically adapts to physiological and pathological conditions in all reproductive organs highlighting the functional plasticity of these cells. Conclusion Macrophage polarization and functions are pivotal in maintaining reproductive health. Hence, understanding the role of macrophages in various reproductive organs provides a foundation for developing new therapies.

ObjectiveThis study aimed to assess whether anti-β2-glycoprotein I (β2GPI)/human leukocyte antigen (HLA)-DR autoantibodies are associated with pregnancy outcomes in women with infertility receiving assisted reproductive technology (ART) in relation to antithrombotic therapies.MethodsIn this multicenter prospective cohort study, levels of anti-β2GPI/HLA-DR autoantibodies were measured in 194 women with infertility, who subsequently received embryo transfer (ET). The rates of clinical pregnancy, biochemical pregnancy loss, live birth, and miscarriage were assessed in relation to antibody positivity and antithrombotic treatments. The primary outcome was to evaluate how antithrombotic treatments were associated with pregnancy outcomes in women with anti-β2GPI/HLA-DR antibodies receiving ART. The treatment modality for the antibody-positive group was determined for each ET at the discretion of the attending physician.ResultsFinally, 30 women in the antibody-positive group and 123 in the antibody-negative group were analyzed. The prevalence of recurrent implantation failure in the antibody-positive group (40.0%, 12/30) was higher than that in the antibody-negative group (20.3%, 25/123; p = 0.024). The clinical pregnancy rate per ET tended to be lower in the antibody-positive group than in the antibody-negative group (30.4%, 21/69 vs 43.6%, 92/211; p=0.053), while the implantation rate per embryo was significantly lower in the antibody-positive group than in the antibody-negative group (26.3%, 21/80 vs 39.0%, 92/236; p=0.040). Among women in the antibody-positive group, low-dose aspirin (LDA), LDA plus unfractionated heparin (UFH), and non-LDA/non-UFH treatments were given in 30, 5, and 34 ET cases, respectively. The clinical pregnancy (42.9%, 15/35 ET vs. 17.6%, 6/34 ET; p = 0.044) and live birth (37.1%, 13/35 ET vs. 11.8%, 4/34 ET; p = 0.030) rates were higher in treated-group with LDA/UFH than non-LDA/non-UFH group. LDA/UFH treatment was independently associated with higher clinical pregnancy rates (adjusted odds ratio, 3.34; 95% confidence interval, 1.02–12.3; p = 0.047). Immunofluorescent staining showed coordinated expression of β2GPI and HLA-DR antigens on the epithelial cells of the eutopic endometrium in the antibody-positive group.ConclusionLDA/UFH treatment may be associated with higher clinical pregnancy and live-birth rates in women positive for anti-β2GPI/HLA-DR antibodies receiving ART.

Purpose:This study investigated the effectiveness of an oral GnRH antagonist for retained products of conception (RPOC) carrying a risk of heavy bleeding. Methods:With IRB approval and patient consent, this retrospective study included 97 RPOC cases after miscarriage. Clinical courses of the GnRH antagonist group (n = 20) were compared with those of non-GnRH antagonist group (historical control, n = 77). Surgical intervention was performed if there is no decrease in RPOC blood flow or size after treatment initiation. Results:The reduction rate in the maximum RPOC diameter after treatment initiation in GnRH antagonist group was greater compared to that in non-GnRH antagonist group [50 (0-79.7)% vs. 15.4 (0-56.9)]%, p < 0.001]. The frequency of surgical intervention in GnRH antagonist group was lower (30.0%, 6/20) than that of non-GnRH antagonist group (70.1%, 54/77, p = 0.002). Multivariate analysis showed that GnRH antagonist reduced the risk of surgical intervention [adjusted-odds ratio (95% confidence interval); 0.20 (0.06-0.58), p = 0.003]. In the GnRH antagonist group, the period from RPOC diagnosis to menstrual resumption was shorter [14.5 (9-71) days] than that of non-GnRH antagonist group [26.0 (6-95) days, p = 0.002]. Conclusion:GnRH antagonist may be a new therapeutic candidate for RPOC.

OBJECTIVE:Marginal cord insertion (MCI) is often defined as an abnormal placental cord insertion (PCI), yet there is limited discussion on the maternal backgrounds and perinatal complications associated with its occurrence. This retrospective cohort study aimed to investigate maternal backgrounds associated with MCI and to compare perinatal outcomes between MCI and normal PCI. MATERIALS AND METHODS:The study included 1038 deliveries from 2021 to 2023 in our institution, examining maternal backgrounds and perinatal outcomes. Multivariable logistic regression analysis was conducted for variables that showed significance in univariate analysis of maternal backgrounds. For perinatal outcomes, variables that exhibited significance were further analyzed using multivariable logistic regression, considering factors previously reported to be associated with those events. RESULTS:9.5 % exhibited MCI. Assisted reproductive technology, nulliparous, and congenital uterine anomalies were identified as independent risk factors for MCI. In perinatal outcomes, fetal growth restriction (FGR) and emergency cesarean section were significantly more prevalent in cases with MCI. Even when compared to factors previously reported to be associated with FGR and emergency cesarean section, MCI remained an independent risk factor. CONCLUSION:In addition to previously reported factors such as ART and primiparity, uterine anomalies were also identified as risk factors for MCI. It is important to manage MCI with the awareness that it increases the incidence of perinatal complications.

Studies have focused on uterine peristalsis and endometrial development, whereas knowledge is limited on cyclical changes in the uterocervical angle (the angle formed between the uterine corpus and cervix) during the menstrual cycle. Here, these dynamic changes were investigated. We conducted a retrospective analysis of 99 freeze-thawed blastocyst transfer cycles in 2020 and a prospective analysis of 192 cycles between 2022 and 2023. Transvaginal ultrasonography was performed to measure the uterine angle during the menstrual, ovulatory, and implantation periods. In the prospective study, conditions were standardized by instructing patients to empty their bladders and avoid uterine compression during scanning. In the retrospective analysis, the uterine angle significantly differed between the menstrual and ovulatory periods (141.1 ± 33.5° vs. 147.7 ± 40.9°, p = 0.04), but no correlation with serum estradiol or progesterone levels was observed. The prospective analysis confirmed significant differences in uterine angle between the menstrual and ovulatory periods and between the ovulatory and implantation periods (135.1 ± 27.7°, 141.5 ± 30.9°, and 136.8 ± 28.7°, respectively; both p < 0.01), without hormonal correlation. These findings suggest that the uterine angle varies throughout the menstrual cycle, becoming more anteverted during the menstrual and implantation periods and straightening around ovulation.

The fibrosis mechanism in endometriosis is not elucidated. We investigated the role of eosinophil in fibrosis of endometriosis. The endometriotic stromal cells (ESCs) and endometrial epithelial cells (EECs) were subjected to in vitro experiments. Within endometriotic lesions, eosinophils were prominently observed by Hematoxylin-Eosin (HE) staining. Immunohistochemical staining for Major Basic Protein (MBP), a granule protein of eosinophils, revealed that MBP-positive eosinophils were predominantly found in the endometrial stromal region beneath the epithelial cell layer. Eosinophil clusters were found in 17 of 18 ovarian endometrioma (EMoma) cases, compared to 3 of 16 in non-endometriotic ovarian cyst/tumor (non-EMoma) (P < 0.0005). HE staining revealed eosinophils in fibrotic areas, and fields with ≥ 3 eosinophils per 100 × 100 μm area showed higher counts of nucleolus-positive fibroblasts (P < 0.05). Serial Masson Trichrome staining revealed blue-stained extracellular matrix around MBP-positive eosinophils, indicating fibrosis. GM-CSF levels, a stimulator of eosinophils, were higher in EMoma contents (93.6 ± 16.9 pg/ml) compared to non-EMoma (3.6 ± 2.1 pg/ml, P < 0.05). Coculture of eosinophils with ESCs or EECs upregulated PAI-1 mRNA and protein expression. Immunohistochemistry confirmed PAI-1 expression in eosinophil-rich lesions. These findings suggest that eosinophils promote fibrosis in endometriosis through PAI-1 induction, offering new therapeutic targets.

The [C11U A ,C11U B ] and [C10U A ,C15U A ] variants of human relaxin-2, which were synthesized via a one-pot assembly of the component A- and B-chains, efficiently reduced the expression of a tissue fibrosis-related factor in endometriotic stromal cells.

IntroductionAnti-β2-glycoprotein I (β2GPI)/human leukocyte antigen (HLA)-DR antibodies may be a risk factor for recurrent pregnancy loss (RPL). The therapeutic modality for women with RPL and anti-β2GPI/HLA-DR antibody positivity has not been evaluated. This prospective, multicenter, observational study aimed to assess whether low-dose aspirin (LDA) and/or heparin therapies improve pregnancy outcomes in women with RPL who tested positive for anti-β2GPI/HLA-DR antibodies.MethodsBetween August 2019 and December 2021, 462 women with RPL underwent anti-β2GPI/HLA-DR antibody measurements and risk assessments for RPL. Each attending physician decided the treatment modality for women with RPL who tested positive for anti-β2GPI/HLA-DR antibodies, and their pregnancy outcomes were followed up until December 2023. Finally, 47 pregnancies in 47 women with RPL and anti-β2GPI/HLA-DR antibody positivity were included in the analysis and were divided into two groups regarding whether they were treated with LDA and/or unfractionated heparin (UFH) (LDA/UFH group, n = 39) or with neither of them (non-LDA/non-UFH group, n = 8). The rates of live birth and pregnancy complications (i.e., preeclampsia and preterm delivery before 34 gestational weeks due to placental insufficiency) were compared between the two groups.ResultsThe live birth rate in the LDA/UFH group was higher than that in the non-LDA/non-UFH group (87.2% vs 50.0%, p = 0.03). The pregnancy complication rate in the LDA/UFH group was significantly lower than that in the non-LDA/non-UFH group (5.9% vs 50.0%, p = 0.048). Among 21 women who tested positive for anti-β2GPI/HLA-DR antibodies and had no other risk factors for RPL, the live birth rate in the LDA/UFH group (n = 14) was much higher than that in the non-LDA/non-UFH group (n = 7) (92.9% vs 42.9%, p = 0.03).DiscussionThis study, for the first time, demonstrated that LDA and/or UFH therapies are effective in improving pregnancy outcomes in women with RPL and aβ2GPI/HLA-DR antibody positivity.

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.