Narrative review on semen and vaginal microbiota links to infertility outcomes

Infertility affects up to 15% of couples worldwide and is influenced by complex biological, immunological, and environmental factors. While reproductive microbiome research has expanded rapidly, the majority of published studies remain largely descriptive, focusing on taxonomic profiling rather than functional or mechanistic insight. Findings from vaginal microbiome studies have been heterogeneous and strongly influenced by methodological variation, and the male genital microbiome has received comparatively less attention, particularly in a couple context. This narrative mini review provides a synthesis of studies investigating paired male and female reproductive microbiomes, emphasizing observational evidence of partner- associated microbial patterns in relation to fertility outcomes. The term ‘seminovaginal’ microbiota is discussed as a hypothesis describing the transient and dynamic interface arising during sexual activity. Current evidence is limited, largely associative, and constrained by insufficient standardization of sampling, sample handling and processing, data analysis, restricting causal interpretation. Addressing these gaps through coupled, longitudinal, and mechanistic study designs is essential for advancing biologically meaningful conclusions in infertility research and reproductive treatments.