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

Abstract

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.

The Complex Interplay between Vaginal Microbiota, HPV Infection, and Immunological Microenvironment in Cervical Intraepithelial Neoplasia: A Literature Review

“…These differences are the result of the coaction of genetic factors, which influence the immunity and metabolic pathways, and cultural and social factors, which influence lifestyle (i.e., hygiene practices) [37]. Female hormones also have a great impact on vaginal microbiota, providing the greatest stability over the menstrual cycle at the time of the estrogen peak [38,39], acting in a similar way to hormonal contraceptives; some studies show their association with a lower risk of incidence and lower recurrence and prevalence of BV [40]. Other environmental factors that influence VMB composition are smoking [41] and recent intercourse [42].…”

Molecular Epidemiology of Genital Infections in Campania Region: A Retrospective Study

“…In this context, specific preventative and protective strategies associated with surveillance programs are urgently needed to face this problem. It is well known that a dysbiotic genital microenvironment with impaired bacterial tolerance and anti-inflammatory mechanisms influences the fertility, course of conception, and outcome of pregnancy, promoting the colonization and invasion of some opportunistic microorganisms or uropathogens that occur more often in women than men due to their anatomical features [ 17 , 31 , 32 ].…”

The gut microbiome, health and personalised nutrition

“…Another factor in gut health is transit time, and constipation often signals problems. Optimal transit time (from fork to loo) was associated with increased microbiome diversity, and so linked to a reduced risk of cardiovascular disease, reduced risk of obesity, better mental health, and cognitive function, as well as fertility, immune health and production of neurotransmitters and hormones 13–16 . Male susceptibility to cardiometabolic disorders earlier in life makes adopting and implementing steps to optimise the gut microbiome important.…”

“…Optimal transit time (from fork to loo) was associated with increased microbiome diversity, and so linked to a reduced risk of cardiovascular disease, reduced risk of obesity, better mental health, and cognitive function, as well as fertility, immune health and production of neurotransmitters and hormones. [13][14][15][16] Male susceptibility to cardiometabolic disorders earlier in life makes adopting and implementing steps to optimise the gut microbiome important. Moreover, the impact the gut microbiome appears to have on male fertility and testosterone availability 17 may be a factor in the considerable decrease in male fertility in the past 50 years.…”