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

Abstract

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.

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

“…Notably, the presence of Bifidobacterium, Prevotella, and Lactobacillus iners in the vagina, along with Solanum torvum, Fusobacterium, and Streptococcus in the cervix, exhibits a negative association with successful pregnancy following in vitro fertilization. [56][57][58] The notion that the vaginal, cervical, and endometrial microbiome affects fertility is gaining support. The transfer of frozen embryos allows optimal endometrial preparation, adapting the transfer at the exact moment to favor implantation.…”

Microbiome in Female Reproductive Health: Implications for Fertility and Assisted Reproductive Technologies

“…For example, the endometrial microbiota is thought to consist of 30%–70% Lactobacillus and other bacteria such as Gardnerella , Bifidobacterium , Flavobacterium , Pseudomonas , Streptococcus , Prevotella , and Atopobium , which vary dependent on the populations [ 128 , 134 , 142 , 143 ]. Some studies have indicated that the cervical and endometrial microbiomes might be involved in ART outcomes, influencing the implantation of embryo and fetal development [ 20 , 21 ].…”

“…The increase of progesterone forms an LD community in FRT, which not only increases the production of lactic acid, but also down-regulates the expression of TLR4, suppressing inflammatory responses in cervicovaginal epithelial cells [ 75 , 156 ]. The LD community in FRT at early pregnancy can be a beneficial factor in preventing fetal rejection during ART [ 20 , 21 ]. In contrast, the NLD community is frequently associated with extensive inflammatory responses, leading to embryo transfer failure in many ART cases [ 20 , 21 ].…”

“…The LD community in FRT at early pregnancy can be a beneficial factor in preventing fetal rejection during ART [ 20 , 21 ]. In contrast, the NLD community is frequently associated with extensive inflammatory responses, leading to embryo transfer failure in many ART cases [ 20 , 21 ]. Despite such importance of microbiome in the FRT, the ART outcomes can be associated with extensive factors beyond microbiota, such as embryo types (frozen or fresh) and quality, maternal age, hormonal level, and standardized approach [ 95 ].…”

Molecular Basis of Müllerian Agenesis Causing Congenital Uterine Factor Infertility—A Systematic Review

“…Infertility can be caused by different factors in males, females, and can be combined or even unexplained [ 3 ]. Common causes in females are diseases of the ovaries, fallopian tubes, uterus, endocrinal, genital tract dysbiosis or combined, and differ from country to country [ 5 ]. Similarly, the cause can commonly be obstruction of the tract, testicular failure of spermatogenesis, poor sperm quality, or endocrinal in males [ 3 ].…”