GENERAL CONCEPTS OF MICROBIOME AND HOLOBIOME. DYSBIOSIS AND SMALL INTESTINAL BACTERIAL OVERGROWTH SYNDROME: CLINICAL SIGNIFICANCE FOR OBSTETRICIAN-GYNECOLOGISTS, REPRODUCTIVE SPECIALISTS, AND ANDROLOGISTS.

This review explores the critical, yet often overlooked, role of the microbiome and holobiont in reproductive health and pathology, focusing on dysbiosis and SIBO. It aims to provide reproductive specialists with a comprehensive understanding of how microbial imbalances impact fertility, pregnancy outcomes, and reproductive disorders, detailing mechanisms and clinical implications. Modern medicine increasingly recognizes the pivotal role of the microbiome in maintaining human health; however, its influence on reproductive function and associated pathologies remains insufficiently explored within a comprehensive context. This review article is dedicated to analyzing the general concepts of the microbiome and holobiont, as well as their clinical significance for obstetricians-gynecologists, reproductive specialists, andrologists, with a particular emphasis on dysbiosis and small intestinal bacterial overgrowth (SIBO). The relevance of this study is underscored by the growing number of cases of infertility, recurrent pregnancy loss, and other reproductive disorders that may be linked to microbial flora imbalance. The review presents contemporary definitions of the microbiome as a microbial community with its sphere of activity, and the holobiont as an integrated system of the host and all associated microorganisms functioning as a single entity. The main functions of the human microbiome are discussed in detail, including support for digestion, immune system education, protection against pathogens, and nutrient production. Special attention is given to the impact of dysbiosis and small intestinal bacterial overgrowth on systemic processes, such as metabolic endotoxemia and increased intestinal permeability, which lead to chronic inflammation and autoimmune reactions. The novelty of this work lies in the systematization of data concerning the interrelationship between gut dysbiosis and reproductive health, including its influence on infertility, implantation failures, polycystic ovary syndrome, endometriosis, spermatogenesis, and the risk of reproductive system oncological diseases. Readers will gain an in-depth understanding of the mechanisms by which microbiome disturbances, particularly small intestinal bacterial overgrowth, can negatively affect male and female fertility. Furthermore, they will learn about potential clinical consequences, such as the development of autoimmune conditions, metabolic disorders, and alterations in the urogenital tract microbiota, which is critically important for specialists in reproductive medicine.