Evidence That the Endometrial Microbiota Has an Effect on Implantation Success or Failure

Abstract

(Abstracted from Am J Obstet Gynecol 2016;215(6):684–703) In 2002, the vaginal microbiota was first identified using molecular methods that allowed detection of nonculturable bacteria. Alterations in vaginal microbiota could have clinical implications for reproductive and obstetric processes.

A pilot study and case reports on endometrial microbiota and pregnancy outcome: An analysis using 16S rRNA gene sequencing among IVF patients, and trial therapeutic intervention for dysbiotic endometrium

“…In our preliminary study, Lactobacillus dominancy was favorable in terms of pregnancy outcome (Table , Table S2), but the result was not as significant as in the previous report . The reasons for this may be due to the limited study numbers, short follow‐up period, ethnic differences, or specific reasons in current Japanese reproductive medicine; no permission to use preimplantation genetic testing for aneuploidy or oocyte donations, and enforcement of single embryo transfer.…”

“…Using the definition by Moreno et al, 47 cases (51.1%) presented LDM (>90% Lactobacillus spp) and 45 cases (48.9%) presented NLDM (<90% Lactobacillus spp with >10% of other bacteria) at initial analysis (Figure ). Nine patients had treatment of NLDM; they initially showed NLDM in their first endometrial microbial analysis but have come to show LDM after the therapeutic interventions against NLDM (Figure A,B).…”

“…The reasons for this may be due to the limited study numbers, short follow‐up period, ethnic differences, or specific reasons in current Japanese reproductive medicine; no permission to use preimplantation genetic testing for aneuploidy or oocyte donations, and enforcement of single embryo transfer. Moreno et al reported that pregnancy outcome could be predicted by the relative abundance of Lactobacilli in EF, and <90% Lactobacilli in the endometrium had an adverse effect on pregnancy. In our study, patients classified as NLDM but having more than 80% Lactobacilli in the endometrium showed good pregnancy outcomes (Figure , Table S2); thus, the percentage of endometrial Lactobacilli >80% might be enough for embryo implantation.…”

“…Lactobacillus species generally dominate the vagina of healthy asymptomatic women, and they presumably play key roles in preventing bacterial vaginosis and other urogenital diseases by lowering the environmental pH through lactic acid production . Also, several reports have suggested that human uterine microbiota is related to implantation success . Moreno et al defined the bacterial status of the endometrium as Lactobacillus ‐dominated microbiota (>90% Lactobacillus spp) or non‐ Lactobacillus ‐dominated microbiota (<90% Lactobacillus spp with >10% of other bacteria), based on the composition of the microbiota in the endometrial fluid comprised of 191 operational taxonomic units (OTU).…”

“…Moreno et al defined the bacterial status of the endometrium as Lactobacillus ‐dominated microbiota (>90% Lactobacillus spp) or non‐ Lactobacillus ‐dominated microbiota (<90% Lactobacillus spp with >10% of other bacteria), based on the composition of the microbiota in the endometrial fluid comprised of 191 operational taxonomic units (OTU). The presence of non‐ Lactobacillus ‐dominated microbiota (NLDM) was associated with significant decrease in implantation, pregnancy, ongoing pregnancy, and live birth rates …”