Does Increased Estrogen Levels Affect The Number of Lactobacillus Spp and Gardnerella vaginalis in The Endometrial Cavity? A Prospective Study

Background: The endometrial microbiome, its composition, and the quantity of some bacteria could be predictors of successful implantation in vitro fertilisation (IVF) treatment. The presence of Lactobacillus, which negatively correlates with pathogenic bacteria, could be a contributing factor to endometrial ecosystem stability. The study aimed to determine whether the quantity of Lactobacillus spp and Gardnerella vaginalis in the endometrium depends on estrogen levels. A secondary aim was to determine whether the decreased number of Lactobacillus spp leads to increased pathogenic bacteria such as Gardnerella vaginalis in the endometrial cavity. Materials and Methods: This prospective study was conducted in a private IVF center in Tuzla, Bosnia and Herzegovina. Participants were recruited from February 2023 to December 2023. The tip of a double-lumen catheter was used to collect samples from the endometrium. QIAamp DNA Mini Kit was used for DNA isolation. A commercial real-time polymerase chain reaction (RT-PCR) kit was used to detect Lactobacillus spp and Gardnerella vaginalis quantitatively. Results: In total, 92 participants were included in the study, 57 in the fresh cycle and 35 in the frozen cycle of IVF. The youngest participant was 18 years old, and the oldest was 45 years old. The mean age of participants was 34.3 years with a standard deviation of 5.7. After RT-PCR, 90 participants had positive tests on Lactobacillus spp, Gardnerella vaginalis was positive in 31 participants. Conclusion: Supraphysiological estrogen levels do not significantly change the quantity of Lactobacillus spp and Gardnerella vaginalis in the endometrial cavity. Decreasing the number of Lactobacillus spp increased the number of pathogenic bacteria Gardnerella vaginalis in the endometrial cavity.