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

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.

Microenvironment of the Lower Reproductive Tract: Focus on the Cervical Mucus Plug

The female lower reproductive tract microbiota is a complex ecosystem comprising various microorganisms that play a pivotal role in maintaining women's reproductive well-being. During pregnancy, the vaginal microbiota undergoes dynamic changes that are important for a successful gestation. This review summarizes the implications of the cervical mucus plug microenvironment and its profound impact on reproductive health. Further, the symbiotic relationship between the vaginal microbiome and the cervical mucus plug is highlighted, with a special emphasis on how this natural barrier serves as a guardian against ascending infections. Understanding this complex host-microbes interplay could pave the way for innovative approaches to improve women's reproductive health and fertility.

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.

Urogenital tract and rectal microbiota composition and its influence on reproductive outcomes in infertile patients

Introduction

Microbiota in the human body are closely related to human diseases. Female urogenital tract and rectal microbes have been considered as important factors affecting female pregnancy, but the mechanism is unknown.

Methods

Cervical, vaginal, urethral, and rectal swabs were collected from 22 infertile patients and 10 controls, and follicular fluid was extracted from 22 infertile patients. The microbial composition of different sampling sites of infertile patients was examined. By comparing the microbial composition difference between infertile patients and controls and combining bioinformatics methods to analyze the potential impact of the female urogenital tract (cervical, vaginal and urethral) and rectal microbial diversity on female infertility and pregnancy outcomes.

Results

Lactobacillus predominated in the female urogenital tract, but its abundance decreased in infertile patients, whereas the abundance of Gardnerella and Atopobium increased. The microbial changes in the urethra had the same trend as that in the vagina. Compared with healthy controls, the cervical and rectal microbial diversity of infertile patients were significantly increased and decreased, respectively. There might be interactions between microbes in different parts of female. Geobacillus thermogeniticans was enriched in the urogenital tract and rectum of infertile patients, and has a good predictive effect on infertility. Compared with infertile patients, L. johnsonii was enriched in the vagina, urethra, and intestine of the control group. L. acidophilus in follicular fluid might be associated with Non-pregnancy.

Conclusion

This study found that the microbial composition of infertile patients was changed compared with that of healthy people. The translocation of Lactobacillus between the rectum and urogenital tract might play a protective barrier role. The changes of Lactobacillus and Geobacillus might be related to female infertility or pregnancy outcome. The study provided a theoretical basis for the future treatment of female infertility from the perspective of microorganisms by detecting the microbial changes associated with female infertility.

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.

Characterization of cervical canal and vaginal bacteria in pregnant women with cervical incompetence

Vaginal and cervical canal bacteria are associated with women’s health and pregnancy outcomes. Here, we compared their composition and characteristics in 37 reproductive-aged Chinese women including 24 pregnant women with cervical incompetence (vaginal and cervical canal bacteria formed Groups A and B, respectively) and 13 healthy pregnant women (vaginal and cervical canal bacteria formed Groups C and D, respectively) using high-throughput sequencing of the V4 region of 16S rRNA gene. The results of alpha and beta diversity analysis, respectively, indicated no statistical differences between Groups A and B (p = 0.32, 0.06), nor Groups B and D (p = 0.69, 0.74); however, differences were found between Groups C and D (p = 0.02, 0.01) and between Groups A and C (p = 0.04, 0.02). PLS-DA analysis showed that the individuals from each group were irregularly distributed according to their clade. Lactobacillus, Bifidobacterium and Ureaplasma were the dominant genera in all groups. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSts) analysis identified 31 Kyoto Encyclopedia of Genes and Genomes (KEGG) orthologs associated with the bacterial communities from the four groups, including membrane transport, folding, sorting and degradation, xenobiotics biodegradation and metabolism, and nucleotide metabolism. We further determined relationships between pregnancy outcomes (Apgar scores) and certain bacterial species. A significant positive correlation was found between Apgar scores and Actinomyces neuii and Anoxybacillus flavithermus in the vagina and cervical canal of pregnant women with cervical incompetence while Bacteroides plebeius, Bifidobacterium pseudopodium and Staphylococcus petrasii in the cervical canal displayed negative correlations with Apgar scores. Moreover, Clostridium fimetarium, Methanobacterium congolense, Pseudomonas chlororaphis, and Psychrobacter nivimaris in the vagina were negatively correlated with Apgar scores. These bacteria may serve as potential biomarkers, however, additional research is warranted to verify their role in clinical outcomes.

Microbiome as a predictor of implantation

PURPOSE OF REVIEW

Review the latest research on the female urogenital microbiome as a predictor of successful implantation.

RECENT FINDINGS

Lactobacillus crispatus seems to be beneficial species in a healthy female genital tract, although the presence of anaerobic bacteria and their impact has yet to be determined. The vaginal microbiome is associated with assisted reproductive technology (ART) outcome in terms of successful implantation and pregnancy. Approaches restoring a dysbiotic vaginal microbiome seem promising. It is questionable if a unique endometrial microbiome exists, given the low bacterial biomass, the invasiveness of endometrial sampling, and its associated high contamination risk. Future studies should focus on the whole microbiome using proteomics and metabolomics, as well as the virome to get a more holistic understanding of its role in reproduction.

SUMMARY

The vaginal and endometrial compartments are being studied to determine a healthy and unhealthy microbiome composition. Defining a healthy composition could provide insight into physiological processes related to the success of embryo implantation. The vaginal microbiome is easily accessible and its composition can be reliably assessed and can be associated with ART outcome. The existence of an endometrial or uterine microbiome is still debated, due to the combination of low biomass and unavoidable high risk of contamination during sampling.

Identifying Predictive Bacterial Markers from Cervical Swab Microbiota on Pregnancy Outcome in Woman Undergoing Assisted Reproductive Technologies

Background and aims: Failure of the embryo to implant causes about three-fourths of lost pregnancies. Female genital tract microbiota has been associated to Assisted Reproductive Technologies (ART) outcomes. The objective of this study was to analyze the microbiota of human cervical swab and to correlate these findings with the ART outcomes. Materials and Methods: In this study, 88 cervical swabs were collected from women undergoing ART cycles, with various causes of infertility, at the beginning of the ART protocols. After microbial DNA extraction, V3–V4 variable regions of the 16S rRNA gene were amplified and sequenced on the Illumina MiSeq platform. PEnalized LOgistic Regression Analysis (PELORA) was performed to identify clusters of bacterial populations with differential abundances between patients with unfavorable and favorable pregnancy outcome groups, respectively. Results: We identified a core of microorganisms at lower taxonomic levels that were predictive of women’s pregnancy outcomes. Statistically significant differences were identified at species levels with Lactobacillus salivarius, Lactobacillus rhamnosus among others. Moreover the abundance of Lactobacillus crispatus and iners, respectively increased and decreased in favorable group as compared to unfavorable group, resulted within the core of microorganisms associated to positive ART outcome. Although the predominance of lactobacilli is generally considered to be advantageous for ART outcome, we found that also the presence of Bifidobacterium (together with the other lactobacilli) was more abundant in the favorable group. Discussion: Cervix is colonized by microorganisms which can play a role in ART outcomes as seen by an overall decrease in embryo attachment rates and pregnancy rates in both fertile and infertile women. If confirmed in a larger cohort, the abundance of these bacteria can be useful not only as a marker of unfavorable pregnancy outcome but also they may open the way to new interventional strategies based on genital tract microbiota manipulation in order to increase the pregnancy rates in woman undergoing assisted reproductive technologies.