Is there a link between recurrent miscarriage and the vaginal microbiota?

A bacterial imbalance in vaginal microbiota is present in women with unexplained recurrent miscarriage, according to a small Chinese study which finally offers new prospects to prevent this painful pregnancy disorder.

 

Between 1 and 2% of women suffer from recurrent miscarriage (at least three successive interrupted pregnancies prior to 12 weeks’ gestation). In the overwhelming majority of cases, the cause is unknown but a vaginal microbiota imbalance (called “dysbiosis”) is suspected to play a role and has already been recognized as a risk factor for premature delivery and low birth weight. On the contrary, a healthy vaginal flora, dominated by lactobacilli, prevents urogenital tract infections (bacterial vaginosis, mycosis, urinary tract infections or sexually transmitted infections) which can potentially cause miscarriages.

Lower abundance of lactobacilli

To test this hypothesis, researchers studied two groups of 10 individuals, one with women suffering from recurrent miscarriage, the other with healthy volunteers. They collected and analyzed vaginal samples, and the results show a significant difference in the microbiota composition: compared to “control” women, the microbiota of patients had a higher content of three bacterial genera. The authors also observed differences in the expression of some cell functional pathways (vitamin metabolism, cell motility...). Although they were not significant, they still raise questions and should be further explored.

Vaginal dysbiosis: cause or consequence?

Further analysis showed that a miscarriage could lead to a significant alteration of the vaginal microbiota composition; and that imbalances within this ecosystem could, in turn, promote the risk of miscarriage. Although they were not able to determine whether the vaginal dysbiosis was a cause or a consequence of miscarriage, Chinese researchers still suggest that bacterial balance of at-risk women should be restored through better health practices or the use of probiotics.

 

Sources:

Zhang F, Zhang T,  Yingying M et al. Alteration of vaginal microbiota in patients with unexplained recurrent miscarriage. Experimental and therapeutic medicine DOI: 10.3892/etm.2019.7337