Often a taboo topic, miscarriage is nevertheless an ordeal for many women and couples.

Generally unexplained, miscarriages could however find their origin in an imbalance of the vaginal microbiota.

What is a miscarriage?

This is a natural termination of pregnancy during the first 5 months. The majority of them take place in the first quarter.

A miscarriage can be detected by:

  • vaginal blood loss (or metrorrhagia);
  • cramps in the lower abdomen (corresponding to uterine contractions);
  • disappearance of the signs of pregnancy.

Many women experience a miscarriage in their lifetime. Indeed, 23 million miscarriages occur each year worldwide, representing 15% of all pregnancies. Thus, almost 10.8% of women have experienced a miscarriage. Some of them also experience recurrent miscarriages: 1.9% have had two and 0.7% have had three. (Quenby et al., 2021)

In a minority of cases, miscarriages are explained by genetic abnormalities, endocrine dysfunction, or an infectious cause. However, most often it is completely accidental and unexplained.

The vaginal microbiota, an essential element of women’s health

The vagina is home to many microorganisms that live in balance and are essential to the well-being and health of women. A healthy vaginal microbiota is 95% dominated by Lactobacilli. These bacteria have a protective role against vaginal infections such as bacterial vaginosis, urinary tract infections, sexually transmitted infections and fungal infections, which are considered frequent causes of miscarriage.

With this in mind, a team of Chinese researchers wanted to understand the potential impact of vaginal microbiota on recurrent miscarriages.

A clinical trial to elucidate the impact of the vaginal microbiota

20 women participated in the study between September 2016 and March 2017 including 10 women who experienced recurrent miscarriages (RM) while the other 10 women, serving as controls, are considered as not concerned by these troubles.

Vaginal secretion samples were collected to analyse and compare the vaginal microbiota of these women.

After sequencing, the bacterial communities of RM women and control women are quite different. Indeed, the vaginal microbiota of RM women was less diverse than that of women in the control group. Furthermore, 3 bacterial phyla seem to differ between the groups: a higher abundance of Firmicutes is noted in the RM group compared to the control group, while a decrease in Actinobacteria and Bacteroidetes is observed.

Regarding bacterial genera, although Lactobacilli remained the dominant genus in both groups, an increase in the taxa Atopobium, Prevotella and Streptococcus and, above all, a decrease in Lactobacilli were observed in the RM group.

Vaginal dysbiosis does appear to exist in RM women.


The researchers also noted differences in the expression of certain cells functional pathways such as cofactor, vitamin or carbohydrate metabolism, although the results were not significant. Further research to explore these facts would be interesting to complement these results.

Dysbiosis of the vaginal microbiota: cause or consequence of miscarriage?

In this study, the results suggest that the presence of disturbances in the vaginal bacterial profile in women with miscarriages may be either a cause or a consequence of an altered composition of the vaginal microbiome. However, it is not possible at this time to make a decision.

To conclude their article, the authors describe some strategies to consider to prevent the development of miscarriages, including lifestyle changes and a probiotic supplementation.



ZHANG F, ZHANG T, MA Y, HUANG Z, HE Y, PAN H, FANG M, DING H. Alteration of vaginal microbiota in patients with unexplained recurrent miscarriage. Exp Ther Med. 2019, 17(5):3307-16