Chromosomally Normal Miscarriage Is Associated With Vaginal Dysbiosis

Emerging evidence supports an association between vaginal microbiota composition and 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 delivering at term.

Early miscarriage, pregnancy loss before 12 weeks, occurs in one in five pregnancies of which half are due to chromosomal abnormalities. Infection is implicated in 66% of late miscarriages, 12–24 weeks, but is less prevalent in early miscarriage.

Pregnancy has a unique and dynamic immunological milieu that is required to support a healthy pregnancy. Initially, a pro-inflammatory state is required for implantation which involves a release of inflammatory mediators inducing tissue injury and repair. Infection may disrupt the immunological synergy at implantation and trigger adverse outcome.

Medical Specialists at the Hammersmith Hospital Campus (London, UK) investigated the vaginal microbial composition and the local immune response in chromosomally normal and abnormal miscarriages and compare this to uncomplicated pregnancies delivering at term. Cervicovaginal fluid samples were collected from each participant from the posterior vaginal fornix. Chorionic villous material was collected at the time of surgical evacuation of the uterus and analyzed for molecular cytogenetics using quantitative fluorescent polymerase chain reaction (QF-PCR) or bacterial artificial chromosomes (BACs).

For molecular cytogenetics using QF-PCR, DNA was amplified using two multiplexes that include a total of 31 markers; assay 1 contains primers for chromosomes 13, 18, 21 and 22, and assay 2, primers for chromosomes 14, 15 and 16 and the X and Y chromosomes. Supplementary markers were used as required. PCR products were separated on an ABI 3100 capillary genetic analyzer (Thermo Fisher, Scientific, Waltham, MA, USA). The KaryoLite bacterial artificial chromosomes-on-Beads (KL-BoBs) assay was performed using a prenatal chromosome aneuploidy and microdeletion detection test kit (Perkin Elmer, Waltham, MA, USA).

DNA extraction was performed and bacterial 16S rRNA gene amplicon sequencing carried out using the Illumina MiSeq platform (Illumina Inc, San Diego, CA, USA). Cytokine analysis was performed by Human Magnetic Luminex Screening Assay (8-plex) (Luminex Corporation, Austin, TX, USA) to measure the concentration of the following analytes: IL-2, IL-4, IL-6, IL-8, TNF-α, IFN-γ, IL-1β, IL-18 and IL-10.

The investigators showed 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).

The authors concluded that vaginal microbiota depleted of Lactobacillus spp. combined with a heightened local inflammatory response, predispose pregnant women to euploid miscarriage. The data presented suggests that there is a group of women who would benefit from antibiotic or pre- or probiotic treatment to reduce the risk of miscarriage. The study was published on January 28, 2022 in the journal BMC Medicine.

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Hammersmith Hospital Campus 
Thermo Fisher, Scientific
Perkin Elmer
Illumina Inc 
Luminex Corporation