Diet-microbiota interactions influence pregnancy success in females undergoing artificial insemination: insights from the vaginal microbiota and Mediterranean diet

Abstract

The vaginal microbiota plays a key role in female fertility, yet its interaction with diet and lifestyle remains unclear. In this study, we aimed to assess the influence of the Mediterranean diet (MD) adherence and the vaginal microbial profile on pregnancy outcomes in females undergoing artificial insemination (AI). Vaginal swabs from 104 participants were analysed using amplicon-based sequencing to assess microbial diversity and composition in relation to pregnancy status and MD adherence. The overall pregnancy rate following artificial insemination was 23.07% (8.65% resulted in pregnancy loss before reaching full term). Dominant species clustered by CSTs, with CST II–V showing typical Lactobacillus dominance, whereas CST IV-B was enriched in G. vaginalis and A. vaginae. Importantly, all CST IV-B women failed to achieve pregnancy, and only a minority of CST V women conceived. Random forest modelling using CST, AI number, MD adherence, AI type, BMI, and age achieved moderate predictive performance for pregnancy, with high sensitivity but low specificity. CSTs, pregnancy status, number of IAs and adherence to the MD explained the greatest proportion of variation in the vaginal microbiota structure by RDA. Pregnant women with high MD adherence harbored higher abundance of Prevotella lymphophilum, Anaerotignum massiliense, and Micrococcus radiotolerans, whereas G. vaginalis characterized non-pregnant women with low MD adherence. Pregnant women showed lower diversity than non-pregnant women. Among women that got pregnant, those who subsequently miscarried exhibited distinct microbial profiles and reduced diversity. Specific taxa such as Aerococcus mediterraneensis, Streptococcus mitis, Peptoniphilus lacrimalis, Staphylococcus hominis were enriched in miscarriage cases, whereas Winkia neuii, Bacillus mojavensis, and a member of Pseudomonota phyla (previously Proteobacteria) were associated with full-term successful pregnancies. These findings highlight the interaction between diet and vaginal microbiota in determining reproductive outcomes, indicating that the MD would affect fertility by modulating microbial communities.