Inmaculada Moreno reviews what is currently known about the link between the endometrial microbiome and IVF results — a field that in a few years has moved from novelty to clinical tool.
The central thesis: the uterine cavity is not sterile, and the composition of its microbiome is associated with implantation outcomes. This shifts attention from "endometrial thickness" to its biological environment.
The key organism is Lactobacillus (notably Lactobacillus crispatus): lactobacillus dominance is associated with better results, whereas its deficiency with worse ones.
A non-lactobacillary, dysbiotic profile is viewed as a factor in repeated implantation failure: altered flora create an environment unfavourable to the embryo.
The assessment tools are the EMMA and ALICE tests from Igenomix: EMMA characterises the microbiome (lactobacillus balance), ALICE detects the pathogens of chronic endometritis.
Chronic endometritis is an important link here: it often runs silently but is associated with both dysbiosis and implantation failure, and therefore deserves targeted diagnosis.
The practical question is when and how to intervene. Moreno discusses the use of antibiotics (for detected pathogens) and probiotics (to restore the lactobacillus profile).
Measure matters: not every shift in flora needs treatment, and "prophylactic" antibacterial therapy for everyone is unjustified — intervention should rest on the test result.
Reproducibility and standardisation are discussed separately: the result depends on sampling technique, transport and laboratory, so it must be interpreted with caution.
Moreno keeps a balance between enthusiasm and evidence: the microbiome–outcome link is real, but not all correction protocols have an equally solid evidence base.
The practical sense for the clinic is to view the microbiome as another layer of endometrial assessment in patients with repeated failures, not as a routine test for all.
The logic is the same as in the rest of the "endometrial" session: from a universal protocol to an individual assessment of the implantation environment in the specific patient.
Moreno separately dwells on study design: some of the contradictions in the literature stem from different sequencing methods and thresholds for defining "dysbiosis," so direct comparison of studies is difficult.
The clinical conclusion is cautious: microbiome correction is justified mainly in patients with repeated failures and confirmed dysbiosis or chronic endometritis, not as a routine step before every transfer.
The upshot: the endometrial microbiome is a meaningful and manageable factor in repeated implantation failure; the key is lactobacillus dominance, diagnosis via EMMA/ALICE and intervention by result, not blindly.
Lactobacillus dominance, the ENMA test, and a personalised antibiotic-probiotic pathway: how far has the evidence for the endometrial microbiome come in IVF? Live-birth data, host-microbial interactions at the GPCR level, and what to do with a dysbiotic sample before transfer.
Senior Principal Investigator and Director of the Education Department at the Carlos Simón Foundation for Research in Women's Health (INCLIVA). A pioneer in the study of the endometrial microbiota and its impact on reproductive outcomes, she develops basic and translational research on the microbiome in human reproduction.
Author of the lecture "Endometrial microbiome and IVF outcomes"
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