Endometrial microbiota in IVF patients: Lactobacillus dominance, pathogen prevalence and recurrence after treatment

Introduction The endometrial microbiota has been recently described as a Lactobacillus dominant environment and lower levels of this genus have been associated with a decrease in implantation and pregnancy rates. Moreover, the detection and overgrowth of several types of microorganisms in the female reproductive tract including bacterial, fungal and viral pathogens have been associated with complications in pregnancy such as miscarriage or preterm birth. Nevertheless, the prevalence of alterations in the endometrial microbiota of patients undergoing infertility treatment has not been thoroughly described yet. Methods The presence of 36 microorganisms including bacteria, fungi and viruses with relevance in reproductive outcome was quantified in endometrial biopsies by Real-Time qPCR. Moreover, a second biopsy was performed in 86 patients after personalized antimicrobial and/or probiotic treatment to evaluate the efficacy of the treatment. Results An altered microbiota was detected in 87.52% of the samples analyzed. A significantly higher presence of pathogens was detected in dysbiotic samples ( Lactobacillus < 90%, p<0.01). More precisely, opportunistic bacterial pathogens were more frequently associated with dysbiosis (p<0.0001). Ureaplasma parvum and Gardnerella vaginalis were the most frequently detected bacterial pathogens, both individually and in combination, while Candida spp and Cytomegalovirus were detected in 8.2% and 1.6% of the samples. In patients that performed a second biopsy after personalized antimicrobial and probiotic treatment, a significant decrease in pathogen presence was observed (p<0.001), although Ureaplasma parvum showed recurrence in some patients. Discussion Our findings suggest that imbalances in the endometrial microbiota are frequent in patients undergoing IVF treatments. Identifying these imbalances and treating them accordingly could potentially improve endometrial environment in these patients.