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

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.

Utility of sexually transmitted infection screening in diagnosing clinical gynaecological conditions using endometrial specimens

Sexually transmitted infections are associated with gynaecological conditions, yet screening algorithms are lacking. The aim was determining the utility of endometrial specimens for chronic gynaecological diagnosis. In a retrospective cohort study of 91 patients (42.8 % CD138-positive), only 5.5 % tested were positive for Ureaplasma parvum. Endometrial STI screening was not useful in a population of low STI prevalence (<10 %), suggesting its value depends on STI prevalence.

Effects of vaginal microbiota on in vitro fertilization outcomes in women with different infertility causes

Backed by advancements in technologies like microbial sequencing, many studies indicate that the vaginal microbiome is a key marker of female reproductive health. However, further studies are still needed to investigate the correlation between vaginal microbiota (VMB) and outcomes of assisted reproductive technology (ART). Therefore, this study compared the VMB of two types of infertile women undergoing in vitro fertilization (IVF) with normal control women during the implantation window period and investigated the effects of VMB characteristics on IVF outcomes. Vaginal swabs from IVF patients (n = 85) were collected before embryo transfer (ET), and vaginal swabs from normal control women (n = 37) were collected during the 6-8 days of ovulation detection. Results showed differences in the vaginal community structure between infertile women with polycystic ovary syndrome (PCOS) and with tubal factor infertility (TFI) undergoing IVF treatment. The results revealed a higher relative abundance of Lactobacillus iners in the non-pregnant group compared with the pregnant group. The results also demonstrated the abundance of Pseudomonas spp. in both non-pregnant groups of infertile women. The findings suggested that the VMB composition affects the IVF outcomes and that the pre-ET high abundance of L. iners may potentially indicate an IVF failure. The abundance of Pseudomonas spp. in the vagina may be an adverse factor for ART pregnancy.

IMPORTANCE

Many studies suggest that vaginal microbiota (VMB) may affect in vitro fertilization-embryo transfer (IVF-ET) outcomes. Assessing VMB before embryo transfer can optimize timing for better assisted reproductive technology (ART) results. This study examined VMB distribution in infertile women undergoing ART using 16S rRNA sequencing. Results revealed that VMB structure impacted ART outcomes in women with polycystic ovary syndrome (PCOS) and tubal factor infertility (TFI) before embryo transfer ([less than or equal to] 24 hours). Lactobacillus iners and Pseudomonas spp. were identified as adverse factors for post-ET pregnancy. The study also showed differences in pre-ET VMB between normal women and women with PCOS and TFI during the ovulatory window. These findings highlight the importance of considering VMB composition to optimize embryo transfer timing and personalize ART treatment based on infertility type, improving the chances of success.

Expert Opinion: Place in Therapy of Probiotics in Infertility and Recurrent Implantation Failure

Infertility is a widespread medical condition, affecting a notable percentage of couples globally, with a rising prevalence in India. While assisted reproductive technologies (ART) provide hope, recurrent implantation failure (RIF) continues to challenge approximately one in 10 couples undergoing in-vitro fertilization (IVF). This expert opinion document intends to highlight the promise of probiotics, particularly from Lactobacillus, as a therapeutic approach for improving fertility and treating RIF. In India, on June 29-30, 2024, a physical expert meeting was organized involving 14 specialists from gynecology, obstetrics, and fertility fields. The role of probiotics in reproductive health was discussed in the meeting with an emphasis on infertility and RIF. All experts agree that microbial dysbiosis characterized by an imbalance among the dominant Lactobacillus species is associated with RIF leading to increased inflammation hence poor reproductive outcomes. Probiotics have emerged as possible therapies that restore microbial equilibrium while reducing inflammation and enhancing the intactness of the genital epithelium barrier. All experts have strongly supported the use of Lactobacillus-based oral probiotic supplementation particularly for preventing miscarriages and maintaining pregnancy. All the experts unanimously agreed that oral probiotic supplementation, particularly Lactobacillus-based, should be considered as a potential method to prevent miscarriages and aid in maintaining pregnancy. They recommend oral probiotic use prior to embryo transfer to enhance implantation and pregnancy rates. This expert opinion emphasizes the value of probiotics as a safe and non-invasive approach to treating infertility and RIF. By fostering a balanced microbiome, probiotics may increase the likelihood of successful pregnancies.

Exploring the Immunological Aspects and Treatments of Recurrent Pregnancy Loss and Recurrent Implantation Failure

Recurrent pregnancy loss (RPL) is defined as the occurrence of two or more consecutive pregnancy losses before 24 weeks of gestation. It affects 3-5% of women who are attempting to conceive. RPL can stem from a variety of causes and is frequently associated with psychological distress and a diminished quality of life. By contrast, recurrent implantation failure (RIF) refers to the inability to achieve a successful pregnancy after three or more high-quality embryo transfers or at least two instances of egg donation. RIF shares several causative factors with RPL. The immunological underpinnings of these conditions involve alterations in uterine NK cells, reductions in M2 macrophages and myeloid-derived suppressor cells, an increased Th1/Th2 ratio, a decreased Treg/Th17 ratio, the presence of shared ≥3 HLA alleles between partners, and autoimmune disorders. Various therapeutic approaches have been employed to address these immunological concerns, achieving varying degrees of success, although some therapies remain contentious within the medical community. This review intends to explore the immunological factors implicated in RPL and RIF and to analyze the immunological treatments employed for these conditions, which may include steroids, intravenous immunoglobulins, calcineurin inhibitors, anti-TNF antibodies, intralipid infusions, granulocyte colony-stimulating factor, and lymphocyte immunotherapy.

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..

PAI-1 promotes human endometrial stromal decidualization via inhibiting VEGFR2/PI3K/AKT signaling pathway mediated F-actin reorganization

Decidualization of endometrial stromal cells is a prerequisite for successful embryo implantation and early pregnancy. Decidualization dysregulation results in implantation failure. In our previous study, we reported that PAI-1 is abnormally downregulated in the endometrial tissue samples of patients with recurrent implantation failure. This study will explore the dynamic expression changes of PAI-1 in the endometrium during the menstrual cycle and its molecular mechanism affecting endometrial decidualization. Our findings indicated that the abundance of PAI-1 increased in the mid-secretory phase and attached a peak in the decidual phase in the endometrium of women with regular menstrual cycles. In human endometrial stromal cells (HESCs), PAI-1 knockdown attenuated endometrial decidualization by upregulating VEGFR2/PI3K/AKT signaling pathway and impaired the F-actin reorganization. Furthermore, axitinib (a VEGFR2 inhibitor) was used to inhibit the VEGFR2 protein activity and the results suggested that it eliminated the effects of PAI-1 on PI3K/AKT signaling pathways and F-actin remodeling. In addition, the interaction between PAI-1 and KNG1 was confirmed by coimmunoprecipitation assay in HESCs. Altogether, PAI-1-KNG1 may enhance the decidualization of endometrium by inhibiting VEGFR2/PI3K/AKT signaling pathway-mediated F-actin reorganization in healthy females.

The Role of the Vaginal and Endometrial Microbiomes in Infertility and Their Impact on Pregnancy Outcomes in Light of Recent Literature

The Human Microbiome Project (HMP), initiated in 2007, aimed to gather comprehensive knowledge to create a genetic and metabolic map of human-associated microorganisms and their contribution to physiological states and predisposition to certain diseases. Research has revealed that the human microbiome is highly diverse and exhibits significant interpersonal variability; consequently, its exact impact on health remains unclear. With the development of next-generation sequencing (NGS) technologies, the broad spectrum of microbial communities has been better characterized. The lower female genital tract, particularly the vagina, is colonized by various bacterial species, with Lactobacillus spp. predominating. The upper female genital tract, especially the uterus, was long considered sterile. However, recent studies have identified a distinct endometrial microbiome. A Lactobacillus-dominated microbiome of the female genital tract is associated with favorable reproductive outcomes, including higher success rates in natural conception and assisted reproductive technologies (ART). Conversely, microbial imbalances, or dysbiosis, marked by reduced Lactobacilli as well as an increased diversity and abundance of pathogenic species (e.g., Gardnerella vaginalis or Prevotella spp.), are linked to infertility, implantation failure, and pregnancy complications such as miscarriage and preterm birth. Dysbiosis can impair the vaginal or endometrial mucosal barrier and also trigger pro-inflammatory responses, disrupting essential reproductive processes like implantation. Despite growing evidence supporting the associations between the microbiome of the female genital tract and certain gynecological and obstetric conditions, clear microbial biomarkers have yet to be identified, and there is no consensus on the precise composition of a normal or healthy microbiome. The lack of standardized protocols and biomarkers limits the routine use of microbiome screening tests. Therefore, larger patient cohorts are needed to facilitate comparative studies and improve our understanding of the physiological microbiome profiles of the uterus and vagina, as well as how dysbiosis may influence clinical outcomes. Further research is required to refine diagnostic tools and develop personalized therapeutic strategies to improve fertility and pregnancy outcomes.

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.

Antibiotics combined with vaginal probiotics in the embryo transfer cycle of infertile patients with chronic endometritis

Introduction

Chronic endometritis (CE) is a prolonged, mild inflammation of the endometrial lining. This study investigated the impact of the impact of antibiotic treatment combined with vaginal Lactobacillus on pregnancy outcomes in infertile patients with CE during frozen embryo transfer (FET) cycles.

Methods

A retrospective analysis was performed on the clinical data of 7,385 patients who underwent FET. After applying the inclusion and exclusion criteria, 254 patients diagnosed with CE were eligible for inclusion. Of these, 119 patients received antibiotics alone, whereas 135 were treated with a combination of doxycycline and vaginal Lactobacillus. All patients underwent embryo transfer within 6 months following treatment. The general characteristics and pregnancy outcomes of the first FET cycle post-treatment were compared between the two groups.

Results

There were no statistically significant differences between the two groups in terms of general characteristics, clinical pregnancy rate, early miscarriage rate, and ectopic pregnancy rate. Patients who received a combination of doxycycline and Lactobacillus showed a higher biochemical pregnancy rate compared to those who received doxycycline alone, though this difference was not statistically significant (70.37% vs. 64.71%, P=0.313). Furthermore, the incidence rate of premature rupture of membranes was lower in the doxycycline-Lactobacillus group than in the doxycycline group (50.00% vs 33.33%, P=0.037).

Conclusions

Although this study observed the potential benefits of the antibiotic and vaginal probiotic treatment regimen in increasing the biochemical pregnancy rate and reducing the incidence of premature rupture of membranes, the current findings are insufficient to recommend the combined use of antibiotics and vaginal Lactobacillus as an intervention to improve reproductive outcomes in infertile patients with CE.

Research Progress on the Impact of Human Chorionic Gonadotropin on Reproductive Performance in Sows

Human chorionic gonadotropin is a glycoprotein hormone produced by human or humanoid syncytiotrophoblasts that differentiate during pregnancy. Due to its superior stability and long-lasting effects compared to luteinizing hormone, it is often used to replace luteinizing hormone to regulate reproductive performance in sows. Human chorionic gonadotropin promotes oocyte maturation, follicle development, and luteinization, thereby increasing conception rates and supporting early embryonic development. In sow reproductive management, the application of human chorionic gonadotropin not only enhances ovulation synchrony but also improves the success rate of embryo implantation by regulating endometrial receptivity and immune mechanisms, significantly enhancing overall reproductive performance. This article primarily reviews the application of human chorionic gonadotropin in sow follicle development, luteal maintenance, and embryo implantation, providing theoretical support for its use in improving reproductive performance in sows.

Utility of culture and molecular methods using AllplexTM Bacterial Vaginosis Plus Assay (SeegeneⓇ) as a tool for endometriosis, infertility and recurrent pregnancy loss diagnosis

Endometriosis, infertility, or recurrent pregnancy loss (RPL) are entities characterised by a decrease in Lactobacillus spp. and an increase in bacterial vaginosis-associated bacteria, (BVAV) according with 16S rRNA sequencing studies. However, the use of nucleic acid amplification tests (NAAT) as a tool for diagnosis algorithms is unknown. Seventy-four patients were included, with a median age of 36.5 years old (IQR: 34-39) including infertility (n=31), endometriosis (n=25), or RPL (n=18), for culturing and NAAT using the Allplex™ Bacterial Vaginosis Plus (ABVP) assay (SeegeneⓇ) with endometrial samples. The objective was determining the utility of ABVP assay for diagnosing the entities. Forty-six microorganisms were isolated from 31 out of 74 patients (41.9 %). Twenty-five endometrial samples (33.8 %) were positive for some targets included in the ABVP-assay, with median Ct value ∼37 (IQR: 31.3-37.1) and Qt value 1.43 Log10copies/reaction (IQR:1.1-2.6). For Lactobacillus species, sensitivity and specificity were 80 % and 84 %, respectively. Gardnerella vaginalis, 63.6 % and 95.7 %. No significant increase in BVAV was detected in any of the gynaecological entities. The ABVP and culture based algorithm did not show utility as a tool for endometriosis, infertility, or RPL diagnosis.

Endometrial Dysbiosis: A Possible Association with Estrobolome Alteration

BACKGROUND/OBJECTIVES

Microbiota modification at the endometrial level can favor gynecological diseases and impair women's fertility. The overgrowth of pathogen microorganisms is related to the contemporary alteration of estrogen-metabolizing bacteria, including β-glucuronidase, thereby enhancing estrogen-related inflammatory states and decreasing anti-inflammatory cells. The possible connection between estrobolome impairment and gynecological diseases has been suggested in animal models. Nevertheless, in humans, coherent evidence on the estrobolome alteration and functionality of the female reproductive tract is still lacking. The objective of this study was to explore alterations in estrogen-related signaling and the putative link with endometrial dysbiosis.

METHODS

Women with infertility and repeated implantation failure (RIF, N = 40) were enrolled in order to explore the putative link between estrogen metabolism and endometrial dysbiosis. Endometrial biopsies were used to measure inflammatory and growth factor molecules. β-glucuronidase enzyme activity and estrogen receptor (ER) expression were also assessed.

RESULTS

Herein, increased levels of inflammatory molecules (i.e., IL-1β and HIF-1α) and decreased levels of the growth factor IGF-1 were found in the endometrial biopsies of patients presenting dysbiosis compared to eubiotic ones. β-glucuronidase activity and the expression of ERβ were significantly enhanced in patients in the dysbiosis group. Interestingly, Lactobacilli abundance was inversely related to β-glucuronidase activity and to ERβ expression, thus suggesting that an alteration of the estrogen-activating enzyme may affect the expression of ERs as well.

CONCLUSIONS

Overall, these preliminary data suggested a link between endometrial dysbiosis and estrobolome impairment as possible synergistic contributing factors to women infertility and RIF.

Microbiota and Recurrent Pregnancy Loss (RPL); More than a Simple Connection

Recurrent Pregnancy Loss (RPL) affects 1-2% of women, and its triggering factors are unclear. Several studies have shown that the vaginal, endometrial, and gut microbiota may play a role in RPL. A decrease in the quantity of Lactobacillus crispatus in local microbiota has been associated with an increase in local (vaginal and endometrial) inflammatory response and immune cell activation that leads to pregnancy loss. The inflammatory response may be triggered by gram-negative bacteria, lipopolysaccharides (LPS), viral infections, mycosis, or atypia (tumor growth). Bacterial structures and metabolites produced by microbiota could be involved in immune cell modulation and may be responsible for immune cell activation and molecular mimicry. Gut microbiota metabolic products may increase the amount of circulating pro-inflammatory lymphocytes, which, in turn, will migrate into vaginal or endometrial tissues. Local pro-inflammatory Th1 and Th17 subpopulations and a decrease in local Treg and tolerogenic NK cells are accountable for the increase in pregnancy loss. Local microbiota may modulate the local inflammatory response, increasing pregnancy success. Analyzing local and gut microbiota may be necessary to characterize some RPL patients. Although oral supplementation of probiotics has not been shown to modify vaginal or endometrial microbiota, the metabolites produced by it may benefit patients. Lactobacillus crispatus transplantation into the vagina may enhance the required immune tolerogenic response to achieve a normal pregnancy. The effect of hormone stimulation and progesterone to maintain early pregnancy on microbiota has not been adequately studied, and more research is needed in this area. Well-designed clinical trials are required to ascertain the benefit of microbiota modulation in RPL.

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.

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.

Metabolomic and microbiome analysis of cervicovaginal mucus in in vitro fertilization-embryo transfer: Toward predicting pregnancy success

Purpose

In the context of in vitro fertilization-embryo transfer (IVF-ET), factors other than egg quality may be key determinants of treatment success, in particular, maternal factors related to uterine endometrial receptivity and unidentified factors. We therefore aimed to analyze the metabolome and microbiome in IVF-ET patients who did and did not achieve pregnancy.

Methods

Cervicovaginal mucus was collected from patients undergoing IVF-ET. Metabolite analysis was conducted by liquid chromatography-mass spectrometry and the microbiota were determined by the polymerase chain reaction using universal 16S-rRNA gene bacterial primers by MiSeq sequencing. Patients were classified as pregnant (N = 10) or nonpregnant (N = 13). Metabolic pathways were examined by MetaboAnalyst.

Results

Three metabolic pathways, including alanine-aspartate-glutamate metabolism, arginine biosynthesis, and cysteine-methionine metabolism, were commonly decreased at the time of embryo transfer irrespective pregnant outcomes. Notably, pyruvate was decreased in the pregnant group. Amino acid metabolites showed inverse correlations with the presence of anaerobic microbiota in the nonpregnant group.

Conclusions

Metabolism decreased during embryo transplantation, with a notable decrease in pyruvate metabolism, particularly in patients who became pregnant. The behavior of metabolites in the pregnant and nonpregnant groups suggests that metabolome analysis in the cervicovaginal mucus may be a diagnostic marker for predicting pregnancy.