Effect of the vaginal microbiome on the pregnancy rate in women receiving assisted reproductive treatment

The effect of vitamin D supplementation and vaginal probiotics on fertility in women with recurrent implantation failure: A randomized clinical trial

Recurrent implantation failure (RIF) is a significant obstacle in assisted reproductive technology, affecting approximately 10 % of couples undergoing in vitro fertilization (IVF). Emerging evidence suggests that vaginal probiotics and vitamin D supplementation may improve reproductive outcomes. This randomized clinical trial evaluated the effects of these interventions on fertility in women with RIF and thin endometrium (<6 mm). A total of 112 women with a history of RIF were randomized into four groups: vaginal probiotics, vitamin D supplementation, a combination of both, or standard IVF treatment (control). The primary outcome was the pregnancy rate, confirmed by β-hCG testing and ultrasound. Secondary outcomes included changes in Th1/Th2 ratio, natural killer (NK) cell activity, and cytokine profiles. The combination group demonstrated the highest pregnancy rate (46.4 %), which was significantly higher compared with the probiotics ((14.2 %), p = 0.008), vitamin D ((17.8 %), p = 0.002), and control groups ((10.7 %), p = 0.003). Only the combination therapy significantly reduced the Th1/Th2 ratio (p < 0.001) and NK cell activity (p < 0.001), while significantly increasing IL-4 and TGF-β and decreasing IFN-γ levels (all p < 0.001). These findings suggest that combined vaginal probiotics and vitamin D supplementation may improve pregnancy outcomes by modulating the immune responses in women with RIF. This dual intervention may represent a promising strategy for enhancing fertility in this population of RIF patients.

The Role of the Genital Tract Microbiome in Human Fertility: A Literature Review

Background/Objectives: Infertility is a multifactorial condition influenced by various factors, including dysbiosis and alterations in the genital tract microbiome. Recent studies emphasize the microbiome's significant role in influencing a woman's fertility potential, thereby affecting the chances of spontaneous conception and the outcomes of assisted reproductive treatments. Understanding the microbial characteristics and unique features of a healthy genital microbiome, as well as how changes in its composition can impact fertility, would allow for a more comprehensive and personalized approach to managing assisted reproductive treatments. The microbiome also influences pregnancy outcomes, and restoring its balance has been shown to improve fertility in infertile couples. The human microbiome plays a key role in maintaining the body's overall health. Disruptions in microbiome balance among women of reproductive age can contribute to a range of pregnancy-related complications, with notable consequences for both maternal and fetal well-being. Emerging research has highlighted a connection between the reproductive tract microbiome and outcomes of assisted reproductive technologies (ART), suggesting that re-establishing a healthy microbial environment may enhance fertility in couples facing infertility. Methods: We conducted a search on PubMed using the keywords "microbiome", "infertility", and "ART" over the past 10 years. This article aims to provide an updated overview of the role of the microbiome in female reproductive health, with a focus on its implications for fertility treatment. Results: The microbiome has a significant role in influencing women's fertility. Conclusions: Understanding the microbiome's impact on fertility and pregnancy outcomes may lead to more effective and personalized approaches in fertility treatments, improving the chances of successful conception and pregnancy.

The influence and association of blood on transfer catheter and vaginal microbiota on pregnancy outcomes in frozen-embryo transfer cycles

The effect of blood and mucus on the catheter on pregnancy outcomes in frozen-embryo transfer (FET) cycles remains relatively under-investigated. To evaluate the influence of the presence of blood and mucus on the transfer catheter, along with the characteristics of vaginal microbiota on pregnancy outcomes in FET cycles, we comprehensively analyzed the clinical data of 816 patients. We meticulously recorded the potential traces of blood and mucus on the catheter following embryo transfer (ET). We examined three key outcome parameters including implantation rate (IR), clinical pregnancy rate (CPR), and biochemical pregnancy rate (BPR). Our results demonstrated that the presence of blood on the catheter was associated with a marked decrease in BPR and CPR, whereas the presence of mucus had no significant impact on BPR, CPR, and IR. To further elucidate whether the influence of blood on the catheter on pregnancy outcomes was mediated by vaginal microbiota imbalance, we examined the vaginal microbiota using 16S rRNA gene sequencing and conducted in-depth statistical analyses and correlation studies. Interestingly, the alpha and beta diversity of the vaginal microbiota between the blood group and non-blood group differed significantly. Importantly, the abundance of Lactobacillus was markedly decreased in the blood group. Our results indicate that the negative effect of the blood on the catheter on pregnancy may be attributed to the imbalance of vaginal microbiota. These results provide new insights into the potential mechanisms underlying the association between vaginal microbiota and blood on the catheter and their impact on pregnancy outcomes in FET cycles.

A nomogram prediction model for embryo implantation outcomes based on the cervical microbiota of the infertile patients during IVF-FET

The microbiota of the female genital tract is crucial for reproductive health. This study aims to investigate the impact of the lower genital tract microbiota on in vitro fertilization and frozen embryo transfer (IVF-FET) outcomes. This study included 131 women aged 20-35 years who underwent their first or second IVF-FET cycle with no obvious unfavorable factors for implantation. Cervical microbiota samples were collected on the embryo transfer day and analyzed using 16S rDNA full-length sequencing. Clinical outcomes were followed up for analysis. Clinical pregnancy (CP) was achieved in 84 patients, and 47 patients experienced non-pregnancy (NP). The cervical microbiota diversity between NP and CP groups showed no significant differences, but some genera such as Halomonas (P = 0.018), Klebsiella (P = 0.039), Atopobium (P = 0.016), and Ligilactobacillus (P = 0.021) were obviously different between the two groups. Notably, there was no significant difference in the abundance of Lactobacillus between the two groups. A nomogram prediction model was developed using the random forest algorithm and logistic regression, including the classification of Halomonas, Atopobium, and Veillonella, as well as the relative abundance of Lactobacillus, to identify high-risk patients with embryo implantation failure. Both internal (area under the curve [AUC] = 0.718, 95% confidence interval [CI]: 0.628-0.807, P < 0.001) and external validation (AUC = 0.654, 95% CI: 0.553-0.755, P = 0.037) of the model performed well. In conclusion, this study established a correlation between cervical microbiota and embryo implantation failure in infertile women undergoing IVF-FET and developed a prediction model that could help in early identification of patients at high risk of implantation failure.IMPORTANCEThis study investigated the potential role of abnormal cervical microbiota in the pathology of implantation failure after in vitro fertilization and frozen embryo transfer (IVF-FET) treatment. Despite nearly half a century of advancements in assisted reproductive technology (ART), the implantation rate of high-quality embryos still hovered around 50%. Moreover, unexplained recurrent implantation failure (RIF) remains a significant challenge in ART. To our knowledge, we first discovered a prediction model for embryo implantation failure, identifying Halomonas and Veillonella as significantly adverse factors for embryo implantation. Despite some limitations, the internal and external validation of the model could bode well for its clinical application prospect. The insights gained from this study pave the way for intervention in the genital tract microbiota prior to IVF-FET, particularly in patients with RIF and RSA.

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.

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.

Understanding the Associations of Urogenital Microbiomes With Fertility and In Vitro Fertilization

Infertility, defined as the inability to establish a clinical pregnancy after a year of regular, unprotected sexual intercourse, impacts 8%-12% of couples worldwide. Many of these couples turn to in vitro fertilization (IVF) to build their families. The success rate of IVF procedures is variable, with estimates of up to 40% of embryo transfers being unsuccessful. Herein we review the existing literature on the role of the female and male urogenital microbiomes and genital inflammation on fertility and IVF outcomes. We discuss the microbiome across the female reproductive tract (FRT) and identify associations with female infertility, female genital tract inflammation, and success of IVF procedures. We also discuss the male urogenital microbiome and the associations between microbial taxa, genital inflammation, and male fertility parameters. Finally, we consider microbial transfer within couples and the impact this may have on fertility and the success of IVF procedures.

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.

The elusive male microbiome: revealing the link between the genital microbiota and fertility. Critical review and future perspectives

There is a growing focus on understanding the role of the male microbiome in fertility issues. Although research on the bacterial communities within the male reproductive system is in its initial phases, recent discoveries highlight notable variations in the microbiome's composition and abundance across distinct anatomical regions like the skin, foreskin, urethra, and coronary sulcus. To assess the relationship between male genitourinary microbiome and reproduction, we queried various databases, including MEDLINE (available via PubMed), SCOPUS, and Web of Science to obtain evidence-based data. The literature search was conducted using the following terms "gut/intestines microbiome," "genitourinary system microbiome," "microbiome and female/male infertility," "external genital tract microbiome," "internal genital tract microbiome," and "semen microbiome." Fifty-one relevant papers were analyzed, and eleven were strictly semen quality or male fertility related. The male microbiome, especially in the accessory glands like the prostate, seminal vesicles, and bulbourethral glands, has garnered significant interest because of its potential link to male fertility and reproduction. Studies have also found differences in bacterial diversity present in the testicular tissue of normozoospermic men compared to azoospermic suggesting a possible role of bacterial dysbiosis and reproduction. Correlation between the bacterial taxa in the genital microbiota of sexual partners has also been found, and sexual activity can influence the composition of the urogenital microbiota. Exploring the microbial world within the male reproductive system and its influence on fertility opens doors to developing ways to prevent, diagnose, and treat infertility. The present work emphasizes the importance of using consistent methods, conducting long-term studies, and deepening our understanding of how the reproductive tract microbiome works. This helps make research comparable, pinpoint potential interventions, and smoothly apply microbiome insights to real-world clinical practices.

The Vaginal Microbiome: Patient- versus Physician-Collected Microbial Swab: A Pilot Study

The composition of the vaginal microbiota prior to an IVF/IVF-ICSI treatment can predict the chance of achieving a pregnancy. To improve clinical applicability and be more patient-friendly, the self-collection of vaginal samples would be preferable. However, the reliability of patient-collected samples compared to physician-collected samples remains unclear. This study compares microbiome outcomes from patient-collected versus physician-collected vaginal samples. This is a prospective pilot study consisting of two cohorts: Cohort I involved patient self-sampling of the vagina, followed by a physician-collected vaginal swab, while Cohort II involved the reversed order of collection. The interspace profiling (IS-Pro) technique was used to analyze the microbiota composition in all samples. From May 2021 to March 2022, a total of 444 samples were collected from n = 222 patients (aged 21-44 years), with Cohort I (n = 109) and Cohort II (n = 113). The vaginal microbiome composition of both cohorts was highly similar, regardless of the sampling order, with a mean cosine similarity of 0.93 (95% CI 0.91, 0.95) in Cohort I and 0.94 (95% CI 0.92, 0.96) in Cohort II. Furthermore, ANOVA analysis revealed no significant differences in bacterial species abundance between physician- and patient-collected samples, nor between first and second sample collections. The self-collection of vaginal samples can be considered comparable to physician-collected samples and indicates a more patient-friendly and convenient collection of the vaginal microbiome in an outpatient clinical setting.

Pilot Study on Next-Generation Sequencing Analysis of Vaginal Microbiota in Clinically Infertile Patients Treated with Probiotics

Background: In this investigation, we aimed to understand the influence of oral probiotic supplementation on the vaginal microbiota of women preparing for assisted reproductive technology (ART) procedures. Given the importance of a healthy microbiome for reproductive success, this study sought to explore how probiotics might alter the bacterial composition in the vaginal environment. Methods: We recruited a cohort of 30 women, averaging 37 years of age (ranging from 31 to 43 years), who were scheduled to undergo ART. Using 16S ribosomal RNA (rRNA) sequencing, we meticulously analyzed the vaginal microbiota composition before and after the administration of oral probiotic supplements. Results: Our analysis identified 17 distinct microorganisms, including 8 species of Lactobacillus. Following probiotic supplementation, we observed subtle yet notable changes in the vaginal microbiota of some participants. Specifically, there was a decrease in Gardnerella abundance by approximately 20%, and increases in Lactobacillus and Bifidobacterium by 10% and 15%, respectively. Additionally, we noted a significant reduction in the Firmicutes/Bacteroidetes (F/B) ratio in the probiotic group, indicating potential shifts in the overall bacterial composition. Conclusions: These preliminary findings suggest that oral probiotic supplementation can induce significant changes in the vaginal microbiota of middle-aged women undergoing ART, potentially improving their overall bacterial profile. Future studies should consider a larger sample size and a narrower age range to validate these results. Investigating factors related to female hormone production could also provide deeper insights. Understanding the effects of probiotics on the vaginal microbiota in patients with ovarian aging may lead to personalized interventions and better reproductive outcomes.

Vaginal dysbiosis - the association with reproductive outcomes in IVF patients: a systematic review and meta-analysis

PURPOSE OF REVIEW

To examine impact of vaginal dysbiosis (VD), including bacterial vaginosis (BV) and aerobic vaginitis (AV) on reproductive outcomes of in vitro fertilization (IVF) patients.

RECENT FINDINGS

BV-bacteria (e.g. Gardnerella ) and AV-bacteria (e.g. Streptococci and Enterococci ) have been identified in the endometrium. However, there is inconclusive evidence whether IVF patients with VD have lower success rates.

SUMMARY

The present systematic review and meta-analysis of PubMed/Medline, until December 2023 included 25 studies, involving 6835 IVF patients. Overall VD was defined as an approximation of community state type IV, including BV and AV-type dysbiosis based on either molecular or microscopy methods. Outcomes were live birth rate (LBR), early pregnancy loss (EPL), clinical pregnancy rate (CPR), and biochemical pregnancy rate (BPR).Vaginal dysbiosis prevalence was 19% [1271/6835, 95% confidence interval (CI) 18-20%]. Six studies examined AV-type dysbiosis with a prevalence of 4% (26/628, 95% CI 3-6%). Vaginal dysbiosis correlates with a higher EPL [relative risk (RR) = 1.49, 95% CI 1.15-1.94] and lower CPR (RR = 0.82, 95% CI 0.70-0.95). No statistically significant impact of VD, BV, or AV was found on LBR and BPR.Thus, the association between VD and reproductive outcome remains puzzling as it is difficult to explain how VD impacts CPR and EPL but not LBR and BPR.

Vaginal microbiota are associated with in vitro fertilization during female infertility

The vaginal microbiome plays an essential role in the reproductive health of human females. As infertility increases worldwide, understanding the roles that the vaginal microbiome may have in infertility and in vitro fertilization (IVF) treatment outcomes is critical. To determine the vaginal microbiome composition of 1411 individuals (1255 undergoing embryo transplantation) and their associations with reproductive outcomes, clinical and biochemical features are measured, and vaginal samples are 16S rRNA sequenced. Our results suggest that both too high and too low abundance of Lactobacillus is not beneficial for pregnancy; a moderate abundance is more beneficial. A moderate abundance of Lactobacillus crispatus and Lactobacillus iners (~80%) (with a pregnancy rate of I-B: 54.35% and III-B: 57.73%) is found beneficial for pregnancy outcomes compared with a higher abundance (>90%) of Lactobacillus (I-A: 44.81% and III-A: 51.06%, respectively). The community state type (CST) IV-B (contains a high to moderate relative abundance of Gardnerella vaginalis) shows a similar pregnant ratio (48.09%) with I-A and III-A, and the pregnant women in this CST have a higher abundance of Lactobacillus species. Metagenome analysis of 71 samples shows that nonpregnant women are detected with more antibiotic-resistance genes, and Proteobacteria and Firmicutes are the main hosts. The inherent differences within and between women in different infertility groups suggest that vaginal microbes might be used to detect infertility and potentially improve IVF outcomes.

Association between bacterial vaginosis, Chlamydia trachomatis infection and tubal factor infertility in Bukavu, Democratic Republic of Congo

BACKGROUND

Tubal factor infertility (TFI) is common in sub-Saharan Africa and often secondary to pelvic inflammatory disease (PID). Anaerobes associated with bacterial vaginosis (BV) are also found in PIDs widely dominated by Chlamydia trachomatis (C. trachomatis), whose role in TFI is better demonstrated than that of BV.

OBJECTIVES

To determine the prevalence of BV and C. trachomatis and to investigate the association between BV, C. trachomatis and TFI.

METHODS

We included 137 patients treated for infertility between January 2020 and November 2021. Cases were defined as women with infertility aged 18-45 years presenting with TFI (n = 52), and controls as infertile women in the same age groups without TFI (n = 85). Data on social habits, life style and infertility parameters were collected, and we performed screening for BV and C. trachomatis. Multiple regression was used to measure associations.

RESULTS

The prevalence of BV and C. trachomatis was 42.3% (58/137) and 23.4% (32/137), respectively. BV (61.5% vs 30.6%, p<0.001) and C. trachomatis (48.1 vs 8.2%, p<0.001) were more frequent in cases of TFI. BV and C. trachomatis increased the risk of TFI approximately 4-fold [aOR: 3.77 (1.61-8.83), p=0.002] and 14-fold [aOR: 13.77 (4.59-41.27), p<0.001], respectively.

CONCLUSION

BV and C. trachomatis infection are strongly associated with TFI in Bukavu. Prevention and screening should be implemented to reduce the risk of TFI.

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.

Role of vaginal microbiota in idiopathic infertility: a prospective study

OBJECTIVE

The causes of idiopathic infertility are still not known; however, it may be associated with microbial etiologies. The present study examines the vaginal microbiota of infertile as well as fertile women longitudinally.

METHODOLOGY

The study was presented and accepted by the Institutional Ethical Committee of Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir (India). An observational, prospective, multicenteric investigation was conducted at the Department of Obstetrics and Gynecology, Government Medical College Jammu, and its affiliated hospitals in Jammu and Kashmir (India). In order to examine the microbial composition, a cohort of 80 female individuals were involved in the screening process. The investigation involved sequencing of the V3-V4 region of 16S rRNA gene, which was subsequently analyzed using the Mothur pipeline.

RESULTS

The study revealed that the vaginal microbiota of infertile women differed from that of healthy women who had previously given birth without any complications. Both populations have variations in their alpha as well as beta diversity and taxonomical composition. The microbial profiles in the cases of infertility are characterized by elevated levels of Gardnerella, Prevotella, Atopobium, and Enterococcus whereas a higher level of Lactobacillus iners was observed in case of fertile women.

CONCLUSION

In conclusion, it can be inferred that the composition of the vaginal microbiome potentially exerts a significant influence on females afflicted with idiopathic infertility.

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.

Longitudinal analysis of vaginal microbiota during IVF fresh embryo transfer and in early pregnancy

IMPORTANCE

Infertility is a global public health issue which leads many couples to seek fertility treatments, of which in vitro fertilization (IVF) is considered to be the most effective. Still, only about one-third of the women achieve live birth after the first IVF embryo transfer (IVF-ET). Factors affecting embryo implantation are poorly known, but the female reproductive tract microbiota may play a key role. Our study confirms the beneficial role of vaginal lactobacilli, especially Lactobacillus crispatus, in the probability of achieving clinical pregnancy and live birth following IVF-ET. Our findings regarding the intra-individual shift of vaginal microbiota between non-pregnancy and pregnancy states are novel and provide new information about the dynamics of microbiota in the early steps of human reproduction. These findings may help clinicians in their attempts to optimize the conditions for ET by microbiota screening or modulation and timing the ET when the microbiota is the most favorable.

Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis

BACKGROUND

A normal chromosomal constitution defined through PGT-A assessing all chromosomes on trophectoderm (TE) biopsies represents the strongest predictor of embryo implantation. Yet, its positive predictive value is not higher than 50-60%. This gap of knowledge on the causes of euploid blastocysts' reproductive failure is known as 'the black box of implantation'.

OBJECTIVE AND RATIONALE

Several embryonic, maternal, paternal, clinical, and IVF laboratory features were scrutinized for their putative association with reproductive success or implantation failure of euploid blastocysts.

SEARCH METHODS

A systematic bibliographical search was conducted without temporal limits up to August 2021. The keywords were '(blastocyst OR day5 embryo OR day6 embryo OR day7 embryo) AND (euploid OR chromosomally normal OR preimplantation genetic testing) AND (implantation OR implantation failure OR miscarriage OR abortion OR live birth OR biochemical pregnancy OR recurrent implantation failure)'. Overall, 1608 items were identified and screened. We included all prospective or retrospective clinical studies and randomized-controlled-trials (RCTs) that assessed any feature associated with live-birth rates (LBR) and/or miscarriage rates (MR) among non-mosaic euploid blastocyst transfer after TE biopsy and PGT-A. In total, 41 reviews and 372 papers were selected, clustered according to a common focus, and thoroughly reviewed. The PRISMA guideline was followed, the PICO model was adopted, and ROBINS-I and ROB 2.0 scoring were used to assess putative bias. Bias across studies regarding the LBR was also assessed using visual inspection of funnel plots and the trim and fill method. Categorical data were combined with a pooled-OR. The random-effect model was used to conduct the meta-analysis. Between-study heterogeneity was addressed using I2. Whenever not suitable for the meta-analysis, the included studies were simply described for their results. The study protocol was registered at http://www.crd.york.ac.uk/PROSPERO/ (registration number CRD42021275329).

OUTCOMES

We included 372 original papers (335 retrospective studies, 30 prospective studies and 7 RCTs) and 41 reviews. However, most of the studies were retrospective, or characterized by small sample sizes, thus prone to bias, which reduces the quality of the evidence to low or very low. Reduced inner cell mass (7 studies, OR: 0.37, 95% CI: 0.27-0.52, I2 = 53%), or TE quality (9 studies, OR: 0.53, 95% CI: 0.43-0.67, I2 = 70%), overall blastocyst quality worse than Gardner's BB-grade (8 studies, OR: 0.40, 95% CI: 0.24-0.67, I2 = 83%), developmental delay (18 studies, OR: 0.56, 95% CI: 0.49-0.63, I2 = 47%), and (by qualitative analysis) some morphodynamic abnormalities pinpointed through time-lapse microscopy (abnormal cleavage patterns, spontaneous blastocyst collapse, longer time of morula formation I, time of blastulation (tB), and duration of blastulation) were all associated with poorer reproductive outcomes. Slightly lower LBR, even in the context of PGT-A, was reported among women ≥38 years (7 studies, OR: 0.87, 95% CI: 0.75-1.00, I2 = 31%), while obesity was associated with both lower LBR (2 studies, OR: 0.66, 95% CI: 0.55-0.79, I2 = 0%) and higher MR (2 studies, OR: 1.8, 95% CI: 1.08-2.99, I2 = 52%). The experience of previous repeated implantation failures (RIF) was also associated with lower LBR (3 studies, OR: 0.72, 95% CI: 0.55-0.93, I2 = 0%). By qualitative analysis, among hormonal assessments, only abnormal progesterone levels prior to transfer were associated with LBR and MR after PGT-A. Among the clinical protocols used, vitrified-warmed embryo transfer was more effective than fresh transfer (2 studies, OR: 1.56, 95% CI: 1.05-2.33, I2 = 23%) after PGT-A. Lastly, multiple vitrification-warming cycles (2 studies, OR: 0.41, 95% CI: 0.22-0.77, I2 = 50%) or (by qualitative analysis) a high number of cells biopsied may slightly reduce the LBR, while simultaneous zona-pellucida opening and TE biopsy allowed better results than the Day 3 hatching-based protocol (3 studies, OR: 1.41, 95% CI: 1.18-1.69, I2 = 0%).

WIDER IMPLICATIONS

Embryo selection aims at shortening the time-to-pregnancy, while minimizing the reproductive risks. Knowing which features are associated with the reproductive competence of euploid blastocysts is therefore critical to define, implement, and validate safer and more efficient clinical workflows. Future research should be directed towards: (i) systematic investigations of the mechanisms involved in reproductive aging beyond de novo chromosomal abnormalities, and how lifestyle and nutrition may accelerate or exacerbate their consequences; (ii) improved evaluation of the uterine and blastocyst-endometrial dialogue, both of which represent black boxes themselves; (iii) standardization/automation of embryo assessment and IVF protocols; (iv) additional invasive or preferably non-invasive tools for embryo selection. Only by filling these gaps we may finally crack the riddle behind 'the black box of implantation'.

Dynamics of Microbiome Changes in the Endometrium and Uterine Cervix during Embryo Implantation: A Comparative Analysis

BACKGROUND The microbiome is the collection of all micro-organisms and their genes, which naturally live in and on the body. The cervical and endometrial bacterial microbiome has previously been reported to affect fertility and influence the outcomes of assisted reproductive therapy (ART), including embryo transfer. This study aimed to evaluate the cervical and endometrial bacterial microbiome in 177 women treated for infertility before, during, and after embryo implantation, and the outcomes. MATERIAL AND METHODS Cervical and endometrial swabs were collected from 177 women diagnosed with infertility at 3 time points: (1) during the initial examination, (2) during implantation, (3) 10-14 days after implantation. Next-generation sequencing (NGS) was used to analyze the bacterial microbiome. Taxonomic identification was performed with the Usearch algorithm. RESULTS There was a significant change in the number of patients with Escherichia coli depending on the collection time. For the first swab collection, there were significant negative relationships between the percentage of Gardnerella vaginalis and Lactobacillus spp. For the second collection, there was a negative relationship between Lactobacillus helveticus and Lactobacillus jensenii. For the third collection, negative relationships were found between Escherichia coli and Lactobacillus spp. A similar distribution of the bacterial microbiome was observed in all 3 swab collections. CONCLUSIONS Lactobacillus spp. were the main bacteria identified in the cervix and endometrium, present before, during, and after successful embryo transfer. E. coli and G. vaginalis reduced the protective effect of Lactobacilli before, during, and after embryo transfer.

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 .

Impact of a Lactobacillus dominant cervical microbiome, based on 16S-FAST profiling, on the reproductive outcomes of IVF patients

Objective

This study assessed the impact of the cervical microbiome on reproductive outcomes in frozen embryo transfer (FET) patients.

Study design

This cross-sectional study included 120 women (aged 20-40 years) undergoing FET. A cervical sample obtained before embryo transfer was analyzed using 16S full-length assembly sequencing technology (16S-FAST), which detects full length 16S rDNA.

Results

We found that >48% of the identified Lactobacillus species were novel. The cervical microbiome was clustered into three cervical microbiome types (CMT): CMT1, dominated by L. crispatus; CMT2, dominated by L. iners; and CMT3, dominated by other bacteria. CMT1 had a significantly higher biochemical pregnancy rate (P=0.008) and clinical pregnancy rate (P=0.006) than CMT2 and CMT3. Logistic analysis showed that compared to CMT1, CMT2 and CMT3 were independent risk factors for biochemical pregnancy failure (odds ratio [OR]: 6.315, 95% confidence interval [CI]: 2.047-19.476, P=0.001; OR: 3.635, 95% CI: 1.084-12.189, P=0.037) and clinical pregnancy failure (OR: 4.883, 95% CI: 1.847-12.908, P=0.001; OR: 3.478, 95% CI: 1.221-9.911, P=0.020). A L. crispatus-dominated group as a diagnostic indicator of biochemical and clinical pregnancy positive had area under the curve (AUC) values of 0.651(P=0.008) and 0.645(P=0.007), respectively. Combining the cervical microbiome with embryonic stage optimized the diagnostic performance for biochemical and clinical pregnancy failure with AUC values of 0.743(P<0.001) and 0.702(P<0.001), respectively. Additionally, relative abundance of L. crispatus predicted biochemical pregnancy positive with AUC values of 0.679(P=0.002) and clinical pregnancy positive with AUC values of 0.659(P=0.003).

Conclusion

Cervical microbiome profiling using 16S-FAST enables stratification of the chance of becoming pregnant prior to FET. Knowledge of the cervical microbiota may enable couples to make more balanced decisions regarding the timing and continuation of FET treatment cycles.

The Impact of the Microbiological Vaginal Swab on the Reproductive Outcome in Infertile Women

BACKGROUND

The thesis on which this paper is based intended to investigate whether the result of the microbiological vaginal swab has an influence on the outcome of the fertility treatment.

METHODS

The microbiological vaginal swabs of patients who received fertility treatment at Saarland University Hospital were evaluated. Depending on the microorganisms detected, the swab result was classified as inconspicuous, intermediate, or conspicuous. The SPSS software was used to determine the correlation between the swab result and the outcome of the fertility treatment.

RESULTS

Dysbiosis was associated with a worse outcome of fertility treatment. The pregnancy rate with a conspicuous swab was 8.6%, whereas it was 13.4% with an inconspicuous swab. However, this association was not statistically significant. Furthermore, an association of endometriosis with dysbiosis was found. Endometriosis was more frequent with a conspicuous swab result than with an inconspicuous result (21.1% vs. 17.7%), yet the correlation was not statistically significant. However, the absence of lactobacilli was significantly associated with endometriosis (p = 0.021). The association between endometriosis and a lower pregnancy rate was also statistically significant (p = 0.006).

CONCLUSION

The microbiological vaginal and cervical swabs can be used as predictors for the success of fertility treatments. Further studies are needed to assess the impact of transforming a dysbiotic flora into a eubiotic environment on the success of fertility treatments.

The Role of Hydrogen-Peroxide (H2O2) Produced by Vaginal Microbiota in Female Reproductive Health

Female reproductive health is strongly associated with healthy vaginal microbiota, which is thought to be ensured by the dominance of certain Lactobacillus species. Lactobacilli control the vaginal microenvironment through several factors and mechanisms. One of them is their ability to produce hydrogen peroxide (H₂O₂). The role of Lactobacillus-derived H₂O₂ in the vaginal microbial community has been intensively investigated in several studies with many designs. However, results and data are controversial and challenging to interpret in vivo. Defining the underlying mechanisms responsible for a physiological vaginal ecosystem is crucial since it could directly affect probiotic treatment attempts. This review aims to summarize current knowledge on the topic, focusing on probiotic treatment possibilities.

A pilot study using unique targeted testing of the urogenital microbiome has potential as a predictive test during IVF for implantation outcome

PURPOSE

This pilot study aimed to develop a methodology characterising the urogenital microbiome as a predictive test in the IVF workup.

METHODS

Using unique custom qPCRs, we tested for the presence of specific microbial species from vaginal samples and First Catch Urines from the male. The test panel included a range of potential urogenital pathogens, STIs, 'favourable bacteria' (Lactobacillus spp.) and 'unfavourable bacteria' (anaerobes) reported to influence implantation rates. We tested couples attending Fertility Associates, Christchurch, New Zealand for their first round of IVF.

RESULTS

We found that some microbial species affected implantation. The qPCR result was interpreted qualitatively using the Z proportionality test. Samples from women at the time of Embryo Transfer who did not achieve implantation had significantly higher percent of samples that were positive for Prevotella bivia and Staphylococcus aureus compared to women who did achieve implantation.

DISCUSSION

The results provide evidence that most other microbial species chosen for testing had little functional effect on implantation rates. The addition of further microbial targets (yet to be determined) could be combined in this predictive test for vaginal preparedness on the day of embryo transfer. This methodology has a substantial advantage of being affordable and easily performed in any routine molecular laboratory. This methodology is most suitable as a foundation on which to develop a timely test of microbiome profiling. Using the indicators detected to have a significant influence, these results can be extrapolated.

CONCLUSION

Using a rapid antigen test, a woman can self-sample prior to embryo transfer and obtain an indication of microbial species present which could influence implantation outcome.

A critical review of the recent concept of artificial mechanical uterus design in relation to the maternal microbiome: An Update to past researches

The microbiome in the female reproductive tract plays an essential role in immune modulation and reproductive health. However, various microbes become established during pregnancy, the balance of which plays a crucial role in embryonic development and healthy births. The contribution of disturbances in the microbiome profile to embryo health is poorly understood. A better understanding of the relationship between reproductive outcomes and the vaginal microbiota is needed to optimize the chances of healthy births. In this regards, microbiome dysbiosis refers to conditions in which the pathways of communication and balance within the normal microbiome are imbalanced due to the intrusion of pathogenic microorganisms into the reproductive system. This review summarizes the current state of knowledge on the natural human microbiome, with a focus on the natural uterine microbiome, mother-to-child transmission, dysbiosis, and the pattern of microbial change in pregnancy and parturition, and reviews the effects of artificial uterus probiotics during pregnancy. These effects can be studied in the sterile environment of an artificial uterus, and microbes with potential probiotic activity can be studied as a possible therapeutic approach. The artificial uterus is a technological device or biobag used as an incubator, allowing extracorporeal pregnancy. Establishing beneficial microbial communities within the artificial womb using probiotic species could modulate the immune system of both the fetus and the mother. The artificial womb could be used to select the best strains of probiotic species to fight infection with specific pathogens. Questions about the interactions and stability of the most appropriate probiotics, as well as dosage and duration of treatment, need to be answered before probiotics can be a clinical treatment in human pregnancy.

Correlations of joint detection of 22 vaginal microbes with routine examination results of vaginal secretions and assisted reproductive outcomes

The correlations of joint detection of 22 vaginal microbes with routine examination results of vaginal secretions and assisted reproductive outcomes were investigated. There were 37 samples with abnormal vaginal microecology in 107 vaginal secretion samples. The top 5 detection rates of microorganisms were Ureaplasma urealyticum (73.83%), Prevotella sp. (70.09%), Gardnerella vaginalis (53.27%), L. crispatus (52.34%) and L. inerts (51.40%). When the levels of Bacillus and hydrogen peroxide in vaginal secretions decreased or pH increased, the abnormal rates of vaginal microecology increased significantly (P < 0.01). The clinical pregnancy rate (53.66%, 22/41) in the women with normal vaginal microecology was higher than that (37.5%, 9/24) with abnormal vaginal microecology. In conclusions, the joint detection of 22 vaginal microbes can quickly and effectively determine whether the vaginal microecology is normal or not. The evaluation of vaginal microecology may be valuable in predicting the assisted reproductive outcomes of infertile women.

The endometrial microbiota of women with or without a live birth within 12 months after a first failed IVF/ICSI cycle

The endometrial microbiota composition may be associated with implantation success. However, a 'core' composition has not yet been defined. This exploratory study analysed the endometrial microbiota by 16S rRNA sequencing (V1-V2 region) of 141 infertile women whose first IVF/ICSI cycle failed and compared the microbiota profiles of women with and without a live birth within 12 months of follow-up, and by infertility cause and type. Lactobacillus was the most abundant genus in the majority of samples. Women with a live birth compared to those without had significantly higher Lactobacillus crispatus relative abundance (RA) (p = 0.029), and a smaller proportion of them had ≤ 10% L. crispatus RA (42.1% and 70.4%, respectively; p = 0.015). A smaller proportion of women in the male factor infertility group had ≤ 10% L. crispatus RA compared to women in the unexplained and other infertility causes groups combined (p = 0.030). Women with primary infertility compared to secondary infertility had significantly higher L. crispatus RA (p = 0.004); lower proportions of them had ≤ 10% L. crispatus RA (p = 0.009) and > 10% Gardnerella vaginalis RA (p = 0.019). In conclusion, IVF/ICSI success may be associated with L. crispatus RA and secondary infertility with endometrial dysbiosis, more often than primary infertility. These hypotheses should be tested in rigorous well-powered longitudinal studies.

The Vaginal Microbiome in Health and Disease-What Role Do Common Intimate Hygiene Practices Play?

The vaginal microbiome is a dynamic, sensitive microenvironment. The hallmark of a 'healthy' vaginal microbiome is currently believed to be one dominated by Lactobacillus spp., which acidifies the vaginal environment and help to protect against invading pathogens. However, a 'normal' microbiome is often difficult, if not impossible, to characterise given that it varies in response to numerous variables, including pregnancy, the menstrual cycle, contraceptive use, diet, ethnicity, and stress. A Lactobacillus-depleted microbiome has been linked to a variety of adverse vaginal health outcomes, including preterm birth (PTB), bacterial vaginosis (BV), and increased risk of sexually transmitted infections. The latter two of these have also been associated with feminine intimate hygiene practices, many of which are practised without any evidence of health benefits. The most extensively studied practice is vaginal douching, which is known to cause vaginal dysbiosis, predisposing women to BV, pelvic inflammatory disease, and PTB. However, little is known of the impact that intimate hygiene practices and associated products have on the vaginal microbiome. This review aims to outline the major factors influencing the vaginal microbiome and common vaginal infections, as well as to summarise current research surrounding the impact of hygiene products and practices on the vaginal microbiome.

Compositional Changes in the Vaginal Bacterial Microbiome of Healthy Pregnant Women across the Three Gestational Trimesters in Ismailia, Egypt

The composition of the vaginal microbiome may lead to adverse pregnancy outcomes. Normal pregnancy is associated with changes in the vaginal bacterial community composition, which tend to be more enriched with one or two Lactobacillus species promoting a healthy vagina and favorable birth outcomes. The aim of the current study was to determine compositional changes in the healthy vaginal microbiome composition during the three trimesters of pregnancy in Ismailia, Egypt using Illumina MiSeq sequencing of the V3-V4 region of the 16S rRNA. The phylum Firmicutes and the genus Lactobacillus dominated across the three trimesters of pregnancy. L. iners was the most abundant species. However, L. coleohominis and L. reuteri represented the least dominant vaginal lactobacilli. Core microbiome analyses showed the Lactobacillus genus and L. iners species to have the highest prevalence in all the samples of our study groups. The phylum Firmicutes was found to be negatively correlated with almost all other vaginal phyla during pregnancy. Likewise, a negative correlation between Lactobacillus and almost all other genera was detected, including significant negative correlations with Dialister and Prevotella. Furthermore, negative correlations of L. iners were detected with almost all other species, including a significant negative correlation with L. helveticus, G. vaginalis, S. anginosus, and S. agalactiae.

Age- and endometrial microbiota-related delay in development of endometrial receptivity

Purpose

We evaluated factors affecting the development of endometrial receptivity according to age and changes in the endometrial microbiota.

Methods

We recruited patients with infertility who underwent transcriptomic analyses of endometrial receptivity and the endometrial microbiome prior to frozen embryo transfer. An endometrial biopsy was performed 108 h after initial progesterone administration.

Results

In 185 tests from 185 eligible patients, the results of endometrial receptivity analysis were receptive in 111 (60.0%) patients and pre-receptive in 74 (40.0%) patients. Compared with receptive patients, pre-receptive patients had significantly older ages (36.0 ± 0.5 vs. 38.2 ± 0.5, p = 0.0021), a smaller proportion of normal Lactobacillus-dominant microbiota (27.9% vs. 12.2%), and a greater proportion of microbiota with ultralow biomass (22.5% vs. 41.9%) (p = 0.0074). Patient age (adjusted odds ratio: 1.08, 95% confidence interval: 1.01-1.16, p = 0.0351) and a microbiome with ultralow biomass (adjusted odds ratio: 3.82, 95% confidence interval: 1.49-9.82, p = 0.0039) were independent predictive factors for pre-receptive endometrium.

Conclusions

Older age was accompanied by a decrease in Lactobacillus-dominant microbiota; aging and endometrial microbiota with ultralow biomass were significantly associated with pre-receptive endometrium. Our findings suggest that the quantity (rather than proportion) of Lactobacillus in the endometrium is important in the development of endometrial receptivity.

Genital Microbiota and Outcome of Assisted Reproductive Treatment-A Systematic Review

The balance between different bacterial species is essential for optimal vaginal health. Microbiome includes the host genome along with microorganism genomes and incorporates the biotic and abiotic factors, reflecting the habitat as a whole. A significant difference exists in the composition and number of the human microbiota in healthy individuals. About one-tenth of the total body microbiota exists in the urogenital tract and these can be identified by microscopy and culture-based methods, quantitative PCR, next generation and whole genome sequencing. The trend of delaying the planning of pregnancy to a later age nowadays has resulted in magnifying the use of assisted reproductive treatment (ART). Hence, genital microbiota and its impact on fertility has generated immense interest in recent years. In this systematic review, we searched the available evidence on the microbiota of the genital tract in women undergoing ART and studied the outcomes of IVF in different microbial compositions. Despite the inconsistency of the studies, it is evident that vaginal, cervical and endometrial microbiota might play a role in predicting ART outcomes. However, there is no clear evidence yet on whether the diversity, richness, quantity, or composition of species in the maternal genital tract significantly affects the outcomes in ARTs.

Vaginom- und „Endometriom“-Diagnostik bei Kinderwunsch

Die molekulare Diagnostik der Vaginal- und Endometriumflora ermöglicht neue Einblicke in die physiologische Besiedlung des weiblichen Genitaltrakts. Wesentlich ist hierbei eine Dominanz von bestimmten Laktobazillenarten bei gleichzeitig geringer Artenvielfalt. Die Bildung von D‑Laktat ist eine entscheidende Voraussetzung für die Abwehr von sexuell übertragbaren Erkrankungen, den Erfolg einer In-vitro-Fertilisation sowie einen ungestörten Schwangerschaftsverlauf. Eine Störung der Flora durch pathogene Bakterienarten mit der Folge des Auftretens einer bakteriellen Vaginose oder einer chronischen Endometritis kann zu Implantationsversagen, Aborten und Frühgeburtsbestrebungen führen. Bei wiederholtem Implantationsversagen ermöglicht eine Mikrobiomdiagnostik – im Gegensatz zur klassischen Kultur, den Amsel-Kriterien oder dem Nugent-Score – einen sehr viel detaillierteren Einblick in die Pathophysiologie, da sich entscheidende Bakterienarten nur schwer oder gar nicht anzüchten lassen. Dies erlaubt eine sehr viel bessere Planung der Therapie zur Wiederherstellung physiologischer Verhältnisse.

Ureaplasma and Prevotella colonization with Lactobacillus abundance during pregnancy facilitates term birth

Ureaplasma and Prevotella infections are well-known bacteria associated with preterm birth. However, with the development of metagenome sequencing techniques, it has been found that not all Ureaplasma and Prevotella colonizations cause preterm birth. The purpose of this study was to determine the association between Ureaplasma and Prevotella colonization with the induction of preterm birth even in the presence of Lactobacillus. In this matched case–control study, a total of 203 pregnant Korean women were selected and their cervicovaginal fluid samples were collected during mid-pregnancy. The microbiome profiles of the cervicovaginal fluid were analyzed using 16S rRNA gene amplification. Sequencing data were processed using QIIME1.9.1. Statistical analyses were performed using R software, and microbiome analysis was performed using the MicrobiomeAnalyst and Calypso software. A positive correlation between Ureaplasma and other genera was highly related to preterm birth, but interestingly, there was a negative correlation with Lactobacillus and term birth, with the same pattern observed with Prevotella. Ureaplasma and Prevotella colonization with Lactobacillus abundance during pregnancy facilitates term birth, although Ureaplasma and Prevotella are associated with preterm birth. Balanced colonization between Lactobacillus and Ureaplasma and Prevotella is important to prevent preterm birth.

Identification of vaginal microbiome associated with IVF pregnancy

The factors that cause a preterm birth (PTB) are not completely understood up to date. Moreover, PTB is more common in pregnancies achieved by in-vitro fertilization (IVF) than in spontaneous pregnancies. Our aim was to compare the composition of vaginal microbiome at 12 weeks of gestation between women who conceived naturally or through IVF in order to study whether IVF PTB-risk could be related to vaginal microbiome composition. We performed an observational, prospective and multicentre study among two public hospitals and a fertility private clinic in Spain. Vaginal swabs from 64 pregnant women at 12 weeks of gestation were collected to analyse the microbiome composition by sequencing the V3-V4 region of the 16S rRNA. Our results showed that the vaginal microbiome signature at 12 weeks of pregnancy was different from women who conceived naturally or through IVF. The beta diversity and the genus composition were different between both cohorts. Gardnerella, Neisseria, Prevotella, and Staphylococcus genus were enriched genus in the vaginal microbiome from the IVF group, allowing us to create a balance model to predict both cohorts. Moreover, at species level the L. iners abundance was higher and L. gasseri was lower in the IVF group. As a conclusion, our findings were consistent with a proposed framework in which IVF pregnancy are related to risk for preterm birth (PTB) suggesting vaginal microbiome could be the reason to the relation between IVF pregnancy and risk for PTB.

Vaginal microbiome of women with adenomyosis: A case-control study

Immune dysregulation can involve invasion and survival of endometrial glands inside the myometrium of the adenomyosis. There is limited available data concerning alterations of the bacterial microbiome in the reproductive tract of adenomyosis women. The present cross-sectional age-matched study aims to compare vaginal microbiota between women with and without adenomyosis. We recruited women with adenomyosis (N = 40) and age-matched women without adenomyosis (N = 40) from the Departments of Obstetrics and Gynaecology, Ramathibodi Hospital Mahidol University, from August 2020 to January 2021. Vaginal swab samples were collected from the participants. DNA isolation and bacterial 16s rDNA gene sequencing and data analyses were then performed. Comparison of the diversity of vaginal microbiota, microbiota composition, and the operational taxonomic unit (OTU) between adenomyosis and non-adenomyosis (control) groups were undertaken. Data from 40 and 38 women with and without adenomyosis, respectively, were analyzed. Alpha-diversity analysis (Chao1 index) at the species level showed higher vaginal microbial richness in the adenomyosis group when compared with the control group (p = 0.006). The linear discriminant analysis effect size technique (LeFSe) indicated an elevated abundance of several vaginal microbial taxa in the adenomyosis group, including Alloscardovia, Oscillospirales, Ruminoccoccaceae, UCG_002, Oscillospiraceae, Enhydrobacter, Megamonas, Moraxellaceae, Subdoligranulum, Selenomonadaceae, and Faecalibacterium. On the other hand, an increase in the abundance of Megaspehera, Fastidiosipila, Hungateiclostridiaceae, and Clostridia was identified in the control group. Vaginal community state type (CST)-III and -IV were dominated in adenomyosis, while only CST-IV was dominated in the non-adenomyosis group. Lactobacillus was the most abundant vaginal microbial in both groups. In this study, the differences in vaginal microbiome profile were noted between adenomyosis and non-adenomyosis group. The increasing of microbial richness was associated with adenomyosis. Nevertheless, further investigations were required to elucidate the mechanisms and apply them for clinical implications.

Probiotic treatment with specific lactobacilli does not improve an unfavorable vaginal microbiota prior to fertility treatment-A randomized, double-blinded, placebo-controlled trial

OBJECTIVE

To investigate whether treatment with proprietary lactobacilli-loaded vaginal capsules improves an unfavorable vaginal microbiome diagnosed using a commercially available test and algorithm.

DESIGN

A randomized, double-blinded, placebo-controlled study was conducted in 74 women prior to undergoing fertility treatment at a single university fertility clinic between April 2019 and February 2021. The women were randomly assigned in a 1:1 ratio to receive one vaginal capsule per day for 10 days containing either a culture of more than 10⁸ CFU of Lactobacillus gasseri and more than 10⁸ CFU Lactobacillus rhamnosus (lactobacilli group) or no active ingredient (placebo group). Vaginal swabs for microbiota analysis were taken at enrollment, after treatment and in the cycle following treatment.

PARTICIPANTS AND METHODS

Women aged 18-40 years who prior to fertility treatment were diagnosed with an unfavorable vaginal microbiota, characterized by either a low relative load of Lactobacillus or a high proportion of disrupting bacteria using the criteria of the IS-pro™ diagnostic system (ARTPred, Amsterdam, the Netherlands), were enrolled in the study. The primary outcome measure was the proportion of women with improvement of the vaginal microbiota after intervention.

RESULTS

The vaginal microbiota improved after intervention in 34.2% of all participants (lactobacilli group 28.9%, placebo group 40.0%), with no significant difference in the improvement rate between the lactobacilli and placebo groups, RR = 0.72 (95% CI 0.38-1.38).

CONCLUSION

This study indicates that administering vaginal probiotics may not be an effective means of modulating the vaginal microbiome for clinical purposes in an infertile population. However, a spontaneous improvement rate of 34.2% over a period of one to three months, confirming the dynamic nature of the vaginal microbiota, indicates that a strategy of postponing further IVF treatment to await microbiota improvement may be relevant in some patients, but further research is needed.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier NCT03843112.

The Role of Genital Tract Microbiome in Fertility: A Systematic Review

The human microbiome plays a crucial role in determining the health status of every human being, and the microbiome of the genital tract can affect the fertility potential before and during assisted reproductive treatments (ARTs). This review aims to identify and appraise studies investigating the correlation of genital microbiome to infertility. Publications up to February 2021 were identified by searching the electronic databases PubMed/MEDLINE, Scopus and Embase and bibliographies. Only full-text original research articles written in English were considered eligible for analysis, whereas reviews, editorials, opinions or letters, case studies, conference papers, and abstracts were excluded. Twenty-six articles were identified. The oldest studies adopted the exclusive culture-based technique, while in recent years PCR and RNA sequencing based on 16S rRNA were the most used technique. Regardless of the anatomical site under investigation, the Lactobacillus-dominated flora seems to play a pivotal role in determining fertility, and in particular Lactobacillus crispatus showed a central role. Nonetheless, the presence of pathogens in the genital tract, such as Chlamydia trachomatis, Gardnerella vaginalis, Ureaplasma species, and Gram-negative stains microorganism, affected fertility also in case of asymptomatic bacterial vaginosis (BV). We failed to identify descriptive or comparative studies regarding tubal microbiome. The microbiome of the genital tract plays a pivotal role in fertility, also in case of ARTs. The standardization of the sampling methods and investigations approaches is warranted to stratify the fertility potential and its subsequent treatment. Prospective tubal microbiome studies are warranted.

Can Lactobacillus spp. Be a Factor Reducing the Risk of Miscarriage?

Pregnancy loss is a common obstetric problem. Significant causes of miscarriage include genetic and epigenetic disorders of the embryo, immunological and endocrine factors, uterine malformations, improper embryo selection, and lifestyle. Perhaps a hitherto underappreciated cause of miscarriage may be an abnormal microbiota composition of the female reproductive system. Lactobacillus spp. is the most common bacteria within the reproductive tract. However, the protective role of Lactobacilli in the vagina has been well described in the literature, while it is still unknown what function Lactobacilli may have in the uterus. Moreover, new research shows that Lactobacillus spp. can have a role in miscarriage. However, both molecular and immunological mechanisms of host-Lactobacillus spp. interactions are not fully understood. Understanding these relationships will help address the importance and extent of the protective role of Lactobacillus spp. in miscarriage.

Molecular detection and genotyping of Enterocytozoon bieneusi in captive foxes in Xinxiang, Central China and its impact on gut bacterial communities

Enterocytozoon bieneusi is a common gastrointestinal parasite that has a broad range of hosts, including birds, mammals, and even humans. The changes of gut bacterial communities have been demonstrated during the course of E. bieneusi. This study aimed to examine the infection status, and assess the zoonotic potential and influence of E. bieneusi on gut bacterial communities of captive foxes in Xinxiang, central China. Fecal samples were collected from 216 captive foxes, and amplification of the internal transcribed spacer (ITS) gene of each sample was performed by nested polymerase chain reaction. E. bieneusi was detected in 48 (22.2%) samples, and five previously reported genotypes CHN-F1 (n = 25), D (n = 18), BEB6 (n = 3), NCF2 (n = 1), and CHN-DC1 (n = 1) were identified, with CHN-F1 being the dominant genotype (25/48, 52.1%). Phylogenetic analysis further revealed that CHN-F1, D, NCF2, and CHN-DC1 genotypes belonged to the zoonotic group 1 of E. bieneusi, whereas BEB6 belonged to group 2. Moreover, sequencing and bioinformatics analysis of the V3-V4 region of 16S rRNA gene in five E. bieneusi-positive and five negative samples showed that gut microbial diversity was higher in the infected animals. In both groups, Firmicutes and Bacteroidetes were the two most abundant phyla, but the Firmicutes/Bacteroidetes ratio was lower in E. bieneusi-positive foxes (7.9:1) as compared with E. bieneusi-negative foxes (5:1). More importantly, at the phylum level, "beneficial bacteria" such as Firmicutes (1.6%) and Bacteroides (5.8%) increased, whereas "opportunistic pathogens" such as Fusobacteria (8.2%) decreased. Similarly, at the genus level, the pathogenic Clostridiaceae_Clostridium (10.0%) decreased, whereas the "beneficial bacteria" Lactococcus (6.6%) increased. These interesting phenomena warrant further investigation.

The role of gut and genital microbiota and the estrobolome in endometriosis, infertility and chronic pelvic pain

BACKGROUND

Endometriosis is a chronic, burdensome condition that is historically understudied. Consequently, there is a lack of understanding of the etiology of the disease and its associated symptoms, including infertility and chronic pelvic pain (CPP). Endometriosis development is influenced by estrogen metabolism and inflammation, which are modulated by several factors including the microbiome and the estrobolome (the collection of genes encoding estrogen-metabolizing enzymes in the gut microbiome). Therefore, there is increasing interest in understanding the role of microbiota in endometriosis etiology.

OBJECTIVE AND RATIONALE

To date, there is no cure for endometriosis and treatment options often are ineffective. This manuscript will review the potential relationship between the microbiome and endometriosis, infertility and CPP and highlight the available data on the microbiome in relation to endometriosis and its related symptoms. The overarching goal of this manuscript is to inform future microbiome research that will lead to a deeper understanding of the etiology of the disease and possible diagnostic modalities and treatments. The potential impact of the microbiome on estrogen regulation modulated by the estrobolome, as well as inflammation and other endometriosis-promoting mechanisms within the genital tract, will be reviewed. The methodological limitations of microbiome-related studies will be critically assessed to provide improved guidelines for future microbiome and clinical studies.

SEARCH METHODS

PubMed databases were searched using the following keywords: endometriosis AND microbiome, infertility AND microbiome, pelvic pain AND microbiome, IVF (in-vitro fertilization) AND microbiome, endometriosis AND infertility. Clinical and preclinical animal trials that were eligible for review, and related to microbiome and endometriosis, infertility or CPP were included. All available manuscripts were published in 2002-2021.

OUTCOMES

In total, 28 clinical and 6 animal studies were included in the review. In both human and animal studies, bacteria were enriched in endometriosis groups, although there was no clear consensus on specific microbiota compositions that were associated with endometriosis, and no studies included infertility or CPP with endometriosis. However, bacterial vaginosis-associated bacteria and Lactobacillus depletion in the cervicovaginal microbiome were associated with endometriosis and infertility in the majority (23/28) of studies. Interpretation of endometrial studies is limited owing to a variety of methodological factors, discussed in this review. In addition, metadata outlining antibiotic usage, age, race/ethnicity, menopausal status and timing of sample collection in relation to diagnosis of endometriosis was not consistently reported. Animal studies (6/6) support a bidirectional relationship between the gut microbiota and endometriosis onset and progression.

WIDER IMPLICATIONS

There is evidence that a dysbiotic gut or genital microbiota is associated with multiple gynecologic conditions, with mounting data supporting an association between the microbiome and endometriosis and infertility. These microbiomes likely play a role in the gut-brain axis, which further supports a putative association with the spectrum of symptoms associated with endometriosis, including infertility and CPP. Collectively, this review highlights the demand for more rigorous and transparent methodology and controls, consistency across the field, and inclusion of key demographic and clinical characteristics of disease and comparison participants. Rigorous study designs will allow for a better understanding of the potential role of the microbiome in endometriosis etiology and the relationship to other disorders of the female reproductive tract.

The Microbial Composition of Lower Genital Tract May Affect the Outcome of in vitro Fertilization-Embryo Transfer

Objective: This work was conducted in order to study the effect of the lower genital tract (vaginal and cervical canal) microbiota on pregnancy outcomes of reproductive-aged women receiving embryo transfer.

Study design: A total of 150 reproductive-aged patients who received the first fresh in vitro fertilization-embryo transfer (IVF-ET) were included in the study. Samples from the vagina and cervical site of each patient were collected separately using sterile swabs before ET. Genomic DNA was pyrosequenced for the V3–V4 regions of the 16S ribosomal RNA gene. Further bioinformatics analysis was performed using QIIME and R package. Pregnancy outcomes were followed and analyzed to compare differences in microbial composition.

Results: The cervical microbiota had a higher Shannon index than the vaginal microbiota, and the microbial composition was different between the two sites. However, the Sorenson index between the two sites within the same individual was 0.370 (0.309–0.400). A total of 89 patients achieved clinical pregnancy after ET, while 61 failed. The Shannon indices and the microbial community of both vaginal and cervical microbiota between pregnant and non-pregnant groups were not significantly different. The relative abundance of Lactobacillus in the vagina and cervical canal did not differ between the two groups. Linear discriminant analysis, random forest analysis, and receiver-operating characteristic curve analysis showed that Bifidobacterium, Prevotella, and Lactobacillus iners in the vagina, as well as Solanum torvum, Fusobacterium, and Streptococcus in the cervix, may be negatively associated with clinical pregnancy after IVF.

Conclusion: The cervical microbiota was more diverse than the vaginal microbiota, but because of anatomical continuity, there was a correlation between the two sites. The microbial composition of the vagina and cervical canal may influence the outcome of IVF-ET, but more samples are needed to verify this conclusion.

Association of the Cervical Microbiota With Pregnancy Outcome in a Subfertile Population Undergoing In Vitro Fertilization: A Case-Control Study

The microorganisms of the reproductive tract have been implicated to affect in vitro fertilization (IVF) outcomes. However, studies on the reproductive tract microbiota of infertile women are limited and the correlation between cervical microbiota and IVF outcome remains elusive. This study aimed to characterize the cervical microbiota of IVF patients undergoing embryo transfer (ET) and assess associations between the cervical microbiota and pregnancy outcomes while exploring the underlying contributing factors. We launched a nested case-control study of 100 patients with two fresh or frozen-thawed cleavage embryos transferred per IVF cycle. Cervical swabs were collected on the day of ET and divided into four groups according to clinical pregnancy outcomes. Variable regions 3 and 4 (V3-V4) of the 16S rRNA gene were amplified and sequenced on the Illumina MiSeq platform. In fresh IVF-ET cycles, the clinical pregnancy group (FP, n = 25) demonstrated higher α diversity (P = 0.0078) than the non-pregnancy group (FN, n = 26). Analysis of similarity (ANOSIM) revealed a significant difference in β diversity between the two groups (R = 0.242, P = 0.001). In frozen-thawed ET cycles, though not significant, similar higher α diversity was found in the clinical pregnancy group (TP, n = 27) compared to the non-pregnancy group (TN, n = 22) and ANOSIM analysis showed a significant difference between the two groups (R = 0.062, P = 0.045). For patients in fresh IVF-ET groups, Lactobacillus, Akkermansia, Desulfovibrio, Atopobium, and Gardnerella showed differentially abundance between pregnant and non-pregnant women and they accounted for the largest share of all taxa investigated. Among them, Lactobacillus was negatively correlated with the other genera and positively correlated with serum estradiol levels. Logistic regression analysis suggested that the composition of the cervical microbiota on the day of ET was associated with the clinical pregnancy in fresh IVF-ET cycles (P = 0.030). Our results indicate that cervical microbiota composition has an impact on the outcome of assisted reproductive therapy.

The impact of the female genital tract microbiome in women health and reproduction: a review

PURPOSE

The aim of this review is to gather the available research focusing on female genital tract (FGT) microbiome. Research question focuses in decipher which is the role of FGT microbiota in eubiosis, assisted reproduction techniques (ARTs), and gynaecological disorders, and how microbiome could be utilised to improve reproduction outcomes and to treat fertility issues.

METHODS

PubMed was searched for articles in English from January 2004 to April 2021 for "genital tract microbiota and reproduction", "endometrial microbiome", "microbiome and reproduction" and "microbiota and infertility". Manual search of the references within the resulting articles was performed.

RESULTS

Current knowledge confirms predominance of Lactobacillus species, both in vagina and endometrium, whereas higher variability of species is both found in fallopian tubes and ovaries. Microbial signature linked to different disorders such endometriosis, bacterial vaginosis, and gynaecological cancers are described. Broadly, low variability of species and Lactobacillus abundance within the FGT is associated with better reproductive and ART outcomes.

CONCLUSION

Further research regarding FGT microbiome configuration needs to be done in order to establish a more precise link between microbiota and eubiosis or dysbiosis. Detection of bacterial species related with poor reproductive outcomes, infertility or gynaecological diseases could shape new tools for their diagnosis and treatment, as well as resources to assess the pregnancy prognosis based on endometrial microbiota. Data available suggest future research protocols should be standardised, and it needs to include the interplay among microbiome, virome and mycobiome, and the effect of antibiotics or probiotics on the microbiome shifts.

Non-Lactobacillus dominance of the vagina is associated with reduced live birth rate following IVF/ICSI: a propensity score-matched cohort study

PURPOSE

Whether the dominant status of vaginal Lactobacillus is associated with IVF/ICSI outcomes.

METHODS

This is a propensity score-matched retrospective cohort study consists of 2285 women undergoing their first fresh autologous IVF cycles. We divided the patients into the Lactobacillus-dominant group and non-Lactobacillus-dominant group based on the abundance of Lactobacillus in Gram-stained vaginal smear examined by microscopy. We compared IVF outcomes between the two groups. We matched Lactobacillus-dominant women with non-Lactobacillus-dominant women by propensity score (PS) to reduce the impact of confounding factors. We evaluated the effect of vaginal Lactobacillus on live birth using univariate and multivariate analysis models. We also conducted interaction and stratified analyses.

RESULTS

Compare to the Lactobacillus-dominant group, the biochemical pregnancy rate (50.12% vs. 57.61%, P = 0.03), clinical pregnancy rate (40.98% vs. 50.82%, P < 0.01), and live birth rate (31.83% vs. 41.22%, P < 0.01) were significantly lower in the non-Lactobacillus-dominant group, the preclinical pregnancy loss rate (18.22% vs. 11.79%, P = 0.05) and preterm birth rate (33.09% vs. 21.59%, P = 0.02) were significantly higher in the non-Lactobacillus-dominant group. However, the miscarriage rate (18.86% vs. 15.67%, P = 0.40) and ectopic pregnancy rate (1.41% vs.1.64%, P = 0.78) were similar between the two groups. Loss dominance of Lactobacillus in the vagina was an independent risk factor for live birth (OR 0.66, 95% CI 0.50-0.88).

CONCLUSIONS

Loss dominance of Lactobacillus in the vagina negatively affects IVF outcomes by decreasing the chances of pregnancy and live birth, increasing risks of preclinical pregnancy loss and preterm birth.

Limitations of 16S rRNA Gene Sequencing to Characterize Lactobacillus Species in the Upper Genital Tract

The endometrial cavity is an upper genital tract site previously thought as sterile, however, advances in culture-independent, next-generation sequencing technology have revealed that this low-biomass site harbors a rich microbial community which includes multiple Lactobacillus species. These bacteria are considered to be the most abundant non-pathogenic genital tract commensals. Next-generation sequencing of the female lower genital tract has revealed significant variation amongst microbial community composition with respect to Lactobacillus sp. in samples collected from healthy women and women with urogenital conditions. The aim of this study was to evaluate our ability to characterize members of the genital tract microbial community to species-level taxonomy using variable regions of the 16S rRNA gene. Samples were interrogated for the presence of microbial DNA using next-generation sequencing technology that targets the V5-V8 regions of the 16S rRNA gene and compared to speciation using qPCR. We also performed re-analysis of published data using alternate variable regions of the 16S rRNA gene. In this analysis, we explore next-generation sequencing of clinical genital tract isolates as a method for high throughput identification to species-level of key Lactobacillus sp. Data revealed that characterization of genital tract taxa is hindered by a lack of a consensus protocol and 16S rRNA gene region target allowing comparison between studies.

Characterization of the vaginal and endometrial microbiome in patients with chronic endometritis

OBJECTIVE

To compare the endometrial and vaginal microbiome of women with and without chronic endometritis.

STUDY DESIGN

A cohort study with 60 patients undergoing assisted reproductive treatment with their own or donated gametes was undertaken. Vaginal and endometrial samples were taken in the cycle prior to embryo transfer. The endometrial and vaginal microbiome was analysed by mass sequencing of the V3V4 region of 16S rRNA gene. Bioinformatics analysis was performed using QIIME2 and MicrobiomeAnalyst packages. Alpha diversity, beta diversity and taxonomic characterization were compared between samples that tested positive and negative for chronic endometritis on CD138 immunohistochemistry.

RESULTS

Different bacterial communities were detected when vaginal and endometrial samples were analysed in patients with and without endometritis diagnosed using CD138 immunohistochemistry. In patients with endometritis, a higher alpha-diversity index was found in vaginal samples (p = 0.15 for the Shannon index) and significant differences were found in endometrial samples (p = 0.01 for the Shannon index). In the beta-diversity analysis, no significant differences were observed between the groups with and without endometritis. Vaginal and endometrial samples from women with endometritis showed a microbiome pattern that was not dominated by Lactobacillus spp. Relative abundance analysis identified Ralstonia and Gardnerella spp. in endometrial samples, and Streptoccoccus and Ureaplasma spp. in vaginal samples of patients diagnosed with chronic endometritis on CD138 immunohistochemistry. When comparing endometrial and vaginal samples diagnosed with endometritis on CD138 immunohistochemistry, both alpha diversity (p = 0.06 for the Shannon index and p = 0.08 for the Simpson index) and beta diversity (p < 0.001) showed significant differences. Lactobacillus spp. (p = 3.76E-4), Ralstonia spp. (p = 8.19E-4), Delftia spp. (p = 0.004) and Anaerobacillus spp. (p = 0.004) were identified in these sample groups.

CONCLUSION

These results demonstrate the existence of a characteristic vaginal and endometrial microbiota in patients with chronic endometritis. Different genera and species were identified in patients with and without chronic endometritis depending on whether the sample was endometrial or vaginal. There is a clear relationship between changes in the vaginal microbiome and chronic endometritis. The microbiota is a continuum throughout the female reproductive tract, so study of the vaginal microbiota could be useful for the diagnosis of diseases of the upper reproductive tract, such as chronic endometritis.

The Association between Vaginal Dysbiosis and Reproductive Outcomes in Sub-Fertile Women Undergoing IVF-Treatment: A Systematic PRISMA Review and Meta-Analysis

Recent advances in molecular microbiology have enabled refined studies of the genital tract microbiota. This constitutes the basis of the present updated systematic review and meta-analysis which investigate vaginal dysbiosis (VD) as defined by either microscopy (e.g., Nugent score for bacterial vaginosis) or molecular methods (qPCR and Next Generation Sequencing) to evaluate the impact of VD on the reproductive outcomes in women undergoing IVF-treatment. A total of 17 studies were included, comprising 3543 patients and with a VD prevalence of 18% (95%CI 17–19). Across all methods, VD is a significant risk factor for early pregnancy loss in IVF (Relative risk (RR) = 1.71 95%CI 1.29–2.27). Moreover, a predefined sub-analysis of studies using molecular methods for VD diagnosis showed a significant reduction in the clinical pregnancy rate when compared to normal vaginal microbiota patients (RR = 0.55 95%CI 0.32–0.93). However, regardless of diagnostic methodology, VD did not significantly influence live birth rate (LBR). In conclusion, molecular tools have provided a more detailed insight into the vaginal microbiota, which may be the reason for the increased adverse effect estimates in IVF patients with molecularly defined VD. However, the quality of evidence was very low across all outcomes according to GRADE and thus, more studies are warranted to understand the impact of VD in IVF.