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

What was reviewed?

This systematic review explored the role of the genital tract microbiome in fertility, with a focus on its impact on both natural conception and assisted reproductive treatments (ARTs), such as in vitro fertilization (IVF). The review aimed to consolidate current research on the microbiome’s correlation with infertility, discussing how dysbiosis in various areas of the genital tract, such as the vagina, cervix, endometrium, and even the fallopian tubes, affects fertility outcomes. The study involved an analysis of 26 selected articles published until February 2021, using methods like PCR and RNA sequencing to examine microbial diversity and its relationship with infertility.

Who was reviewed?

The review included studies on women and couples with infertility, focusing on those who were either attempting to conceive naturally or undergoing ART treatments. These studies compared the microbiomes of infertile women with those of fertile women and examined the differences in microbial compositions, particularly in the vaginal, cervical, and endometrial environments. Additionally, the review included studies that explored how microbial imbalances could affect ART success rates, such as implantation and pregnancy rates in IVF treatments.

What were the most important findings?

The review highlighted that the genital tract microbiome plays a pivotal role in fertility, particularly the vaginal microbiome. Lactobacillus species, especially Lactobacillus crispatus, were consistently identified as crucial for maintaining a healthy environment conducive to fertility. A Lactobacillus-dominated microbiota was associated with better fertility outcomes, while dysbiosis, characterized by a reduction in Lactobacillus and an overgrowth of pathogens like Gardnerella vaginalis, Ureaplasma species, and other Gram-negative bacteria, was linked to infertility and poor ART outcomes. Notably, the presence of pathogens such as Chlamydia trachomatis and Gardnerella vaginalis was associated with infertility, even in the absence of symptoms like bacterial vaginosis (BV), suggesting that asymptomatic infections still have a significant impact on fertility. The review also discussed how vaginal and endometrial microbiomes could differ, with non-Lactobacillus-dominated endometrial microbiomes correlating with lower rates of implantation and pregnancy in IVF cases. Importantly, no studies were identified that focused on the microbiome of the fallopian tubes, highlighting an area for future research.

What are the greatest implications of this review?

The greatest implication of this review is that clinicians should consider the genital tract microbiome as a factor in infertility assessments and treatments. Dysbiosis, particularly a lack of Lactobacillus dominance, could serve as a diagnostic marker for fertility issues, and addressing microbiome imbalances through interventions such as probiotics or antibiotics could improve fertility outcomes. The review also emphasizes the need for standardized microbiome sampling and analysis methods to allow for more consistent and reliable clinical applications. Additionally, the importance of the vaginal microbiome, specifically Lactobacillus crispatus, as a predictor for ART success points to potential personalized treatments based on individual microbiome profiles, enhancing the precision of fertility treatments.