Intrauterine Growth Restriction Is Associated with Unique Features of the Reproductive Microbiome

Intrauterine growth restriction (IUGR) is an obstetrical complication with an increased risk of perinatal mortality and morbidity. The uterus, once considered to be a sterile environment, has now been described in recent microbiome studies to harbor diverse commensal placenta microbiota, as well as potentially pathogenic flora known to cause infection. Therefore, in this pilot study, we tested whether IUGR was associated with changes to the reproductive microbiome. The reproductive microbiome was surveyed using 16S sequencing (20 IUGR, 20 controls). Alpha and beta diversity were compared, and differential taxa features associated with IUGR were identified. Microbial screening of the placenta demonstrated a diverse range of flora predominantly including Proteobacteria, Fusobacteria, Firmicutes, and Bacteroidetes. Neither alpha- nor beta-diversity was significantly different by IUGR status. However, at the taxa level, IUGR patients had significantly higher prevalence of Neisseriaceae, mucosal β-hemolytic bacteria known to uptake iron-bound host proteins including hemoglobin. Moreover, the increase in anaerobic bacteria such as Desulfovibrio reflects the emergence of a hypoxic environment in the IUGR placenta. Further analysis of the reproductive microbiome of IUGR samples showed lower levels of H₂0₂-producing Bifidobacterium and Lactobacillus that switch from respiration to fermentation, a less energetic metabolic process, when oxygen levels decrease. Source tracking analysis showed that the placental microbial contents were predominantly contributed from an oral source, as compared to a gut or vaginal source. Our results suggest that the reproductive microbiome profiles may, in the future, constitute potential biomarkers for fetal health during pregnancy, while Neisseriaceae may constitute promising therapeutic targets for IUGR treatment.