P–333 Vaginal and endometrial microbiota: is there any correlation
Authors: Voroshilina E , Plotko E , Islamidi D , Koposova O , Zornikov D 
Published: August 2021

Abstract

Study question
Is there any correlation between the total bacterial load and the lactobacilli quantities in the vaginal and endometrial microbiomes in reproductive-age women?

Summary answer
There was no correlation between the vaginal and endometrial total bacterial loads and only a weak positive correlation between the quantities of lactobacilli.

What is known already
The Lactobacilli-dominated microbiota is considered to be the most favorable type of microbiota in the uterine cavity. It is associated with increased reproductive success in women undergoing in vitro fertilization. Whereas the non-Lactobacillus dominated microbial communities are more frequent in women with poor pregnancy outcomes.
When analyzing endometrial microbiota, one of the challenges is sampling. Transvaginal sample intake involves the possibility of contaminating the samples with vaginal microbiota. Moreover, it is an invasive procedure leading to the development of infectious inflammatory diseases of the upper genital tract. Thus, researchers are currently searching for predictors of the state of endometrial microbiota.

Study design, size, duration
It is a cross-sectional study of the vaginal end endometrial micorbiomes from 64 reproductive-age women. Endometrial and vaginal samples were collected simultaneously on days 7–10 of the menstrual cycle. To avoid contamination by vaginal microbiota, Endobrush Standard for Endometrial Cytology (Laboratoire C.C.D.; France) was used for endometrial sampling.

Participants/materials, setting, methods
The study included women who came to the “Garmonia” Medical Center (Yekaterinburg, Russia) seeking infertility treatment. The average age of the patients was 32.2±5.0.
DNA from vaginal and endometrial samples was extracted using PREP-NA-PLUS kit (DNA-Technology, Russia). Vaginal and endometrial microbiota was analyzed using Femoflor real-time PCR kit and DTprime 4M1 thermocycler (DNA-Technology, Russia).

Main results and the role of chance
Total bacterial load (TBL) in vaginal discharge was 3.8–7.9 lg (median — 7.1, interquartile range — 6.6–7.4). TBL in the endometrial samples was 0–5.1 lg (median — 3.9, interquartile range — 3.6–4.2). There was no correlation between TBL values in vaginal discharge and endometrial samples (Spearman’s rho — 0.247, p = 0.049).
Lactobacilli quantities in vaginal discharge were 4.5–8.3 lg (median — 7.2, interquartile range — 6.4–7.6), in endometrial samples — 0–5.1 lg (median — 3.7, interquartile range — 3.1–4.2). There was a weak positive correlation between lactobacilli quantities in vaginal and endometrial samples (Spearman’s rho — 0.362, p = 0.003).
The proportion of lactobacilli in vaginal discharge was 1–100% (median — 100%, interquartile range — 95–100%), in the endometrial samples — 0–100% (median — 96%, interquartile range — 25–100%). There was no correlation between lactobacilli proportions in vaginal and endometrial samples (Spearman’s rho — 0.225, p = 0.074). Furthermore, there was no correlation between lactobacilli quantity in the vagina and their proportion in the endometrial microbiota (Spearman’s rho — 0.294, p = 0.018).
There was only a weak positive correlation between the quantities of lactobacilli in vaginal and endometrial samples. Vaginal TBL values and lactobacilli proportions did not correlate with lactobacilli quantities and proportions in the endometrial samples.

Limitations, reasons for caution
The study was conducted on a small sample. Moreover, it is notoriously difficult to interpret the analysis results for endometrial microbiota due to the high risk of contamination and its low microbial biomass.
Wider implications of the findxings: Apparently, there is no obvious link between the vaginal and endometrial microbiomes. It is possible that, apart from vaginal microbiota, there are other predictors which could allow us to assume whether lactobacilli are present in the endometrial microbiota.

Trial registration number
Not applicable