Systematic analysis of microbiota in pregnant Chinese women and its association with miscarriage.

Background: Miscarriage is the most common adverse pregnancy outcome and more than 50% of its incidence remains unexplained. Earlier studies have suggested that maternal microbiota might be associated with miscarriage, but the association is insufficiently understood.

Methods: We used 16S ribosomal RNA (rRNA) amplicon sequencing and metagenomic sequencing technology to characterize the bacterial composition of three sites including the rectum, vagina, and cervix of a case group of 63 pregnant women who had miscarried compared to a control group of 24 pregnant women who underwent voluntary elective abortion.

Results: The alpha-diversity from the rectum and cervix was significantly decreased in the case group relative to the control group. However, we did not find significant differences in microbial diversity of vaginal samples between the two groups. was the most predominant genus in the cervix and vaginal samples. Gestational age at the time of surgery was positively associated with the rectum microbiota diversity, with an effect size of 10% (P=0.004). Host factors including gestational age and red blood count (RBC) were associated with the rectal microbiota diversity.

Conclusions: We detected a significantly lower rectal microbiota diversity and a pro-inflammatory tendency in the miscarriage group. This is the first study to investigate the association of microbiota from samples collected from three sites and miscarriage. Further studies are warranted to explore further the role of microbiota in miscarriage.