Temporal and Spatial Variation of the Human Placental Microbiota During Pregnancy

Previously believed sterile, the placenta hosts distinct microbial species across various locations. This study aims to elucidate the temporal and spatial variations of placental microbiota throughout gestation, addressing gaps in current understanding.

A case-control study at a single-center compared microbial profiles in pregnant women delivering preterm (<37 weeks) or at term (>37 weeks) across placental sites: basal plate, fetal membranes, and placental villous. Microbial abundance and diversity were evaluated using QIIME and the R package "Phyloseq," while Q-PCR with specific primers validated absolute abundance in samples.

We found no alteration in bacterial communities based on delivery mode across all samples. Q-PCR detected low-abundance bacteria, notably enriched in preterm samples, especially in early preterm cases. Throughout gestation, bacterial composition varied, with increasing levels of Proteobacteria and Firmicutes observed in the placenta. Significant differences in bacterial profiles were noted across locations and gestational stages, with Ralstonia insidiosa consistently present in the basal plate throughout gestation. Species-specific Q-PCR confirmed the presence of Ralstonia and revealed an inverse relationship between Streptococcus agalactiae and pregnancy progression.

The placenta hosts its own microbiome, with distinct profiles observed between term and preterm samples. Further research is needed to clarify the impact of bacterial dysbiosis on preterm birth and develop methods to distinguish pathological bacteria from the natural microbiome.