A recent study published in BMC Medicine finds that changes to a mother's vaginal microbiome may be associated with pregnancy loss.
Miscarriage is the most common type of pregnancy loss and often occurs because the foetus isn't developing normally. Symptoms include fluid, blood or tissue passing from the vagina and pain in the stomach or lower back. It's also common to feel sadness or grief.

Emerging evidence supports an association between vaginal microbiota composition and the risk of miscarriage; however, the underlying mechanisms are poorly understood. We aim to investigate the vaginal microbial composition and the local immune response in chromosomally normal and abnormal miscarriages and compare this to uncomplicated pregnancies delivered at term.
They used 16S rRNA gene-based metataxonomics to interrogate the vaginal microbiota in a cohort of 167 women, 93 miscarriages (54 euploid and 39 aneuploids using molecular cytogenetics) and 74 women who delivered at term and correlate this with the aneuploidy status of the miscarriages. We also measured the concentrations of IL-2, IL-4, IL-6, IL-8, TNF-α, IFN-γ, IL-1β, IL-18 and IL-10 in cervical vaginal fluid.
The results of the study are as follows:
Researchers show that euploid miscarriage is associated with a significantly higher prevalence of Lactobacillus spp. deplete vaginal microbial communities compared to aneuploid miscarriage (P = 0.01). Integration of matched cervicovaginal fluid immune profiles showed that Lactobacillus spp. depleted vaginal microbiota associated with pro-inflammatory cytokine levels most strongly in euploid miscarriage compared to viable term pregnancy (IL-1β; P < 0.001, IL-8; P = 0.01, IL-6; P < 0.001).

Thus, the researchers concluded that their data suggest the vaginal microbiota plays an important aetiological role in euploid miscarriage and may represent a target to modify the risk of pregnancy loss.
Reference:
Chromosomally normal miscarriage is associated with vaginal dysbiosis and local inflammation by Karen Grewa et al. published in the BMC Medicine.
https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-021-02227-7#Abs1