A type of vaginal dysbiosis for each type of infertility?
The role of the vaginal microbiota in infertility has been confirmed: not only does dysbiosis vary with the type of infertility, but bacterial and viral co-infections may contribute cumulatively to infertility.
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Infertility, which affects about 15% of couples of reproductive age, seems to be strongly linked to dysbiosis of the vaginal microbiota.
However, few studies have previously looked into the differences in vaginal microbiota between women presenting with primary infertility (inability to become pregnant after trying for 12 months) and secondary infertility (difficulty becoming pregnant again after a first pregnancy).
Hence the recent work 1 aimed at characterizing the dysbiotic vaginal microbiota and its connection to infertility in 136 Mexican women diagnosed with primary infertility (58 women) or secondary infertility (78).
17.5% Infertility affects approximately 17.5% of the adult population—that is, about one person in six worldwide. Its prevalence varies little from one region to another or according to the wealth of the country. ²
48 million Infertility affects 48 million couples worldwide. The causes, sometimes unexplained, include hormonal, genetic and environmental factors affecting men as well as women. ³
The effect of age
The analysis of vaginal samples showed that age is the primary factor explaining the type of vaginal flora in women in the study.
Age also appears to be positively correlated with primary infertility (the oldest patients were the most affected) and inversely correlated with secondary infertility.
However, as the researchers point out, the vaginal microbiota evolves over the course of life, particularly with a reduction in protective Lactobacillus and an increased sensitivity to dysbiosis. Therefore, the researchers advanced the hypothesis (yet to be validated) that evolution of the microbiota could explain difficulties conceiving, naturally or with assistance, and thus the increased prevalence of primary infertility among older women.
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Two types of infertility, two types of microbiota
In addition, analysis of the vaginal microbiota showed a lower predominance of lactobacilli in women affected by infertility, compared to the flora of fertile women.
But above all, it showed differences between women suffering from primary and secondary infertility.
- In women suffering from primary infertility, beneficial Lactobacillus crispatus and Lactobacillus gasseri were dominant, but researchers also noted an elevated proportion of Gardnerella vaginalis and Fannyhessea vaginae, bacteria that are both implicated in vaginosis. The presence of G. vaginalis is also strongly associated with HPV.
- In the case of secondary infertility, the presence of G. vaginalis goes hand in hand with that of the Epstein-Barr virus and even of Haemophilus influenzae. Sexually transmitted bacteria, some of them already associated with infertility, are also present in greater numbers: Ureaplasma parvum, Ureaplasma urealyticum, Mycoplasma hominis and Chlamydia trachomatis.
Two research pathways
These results suggest that the composition of the vaginal microbiota could play a decisive role in infertility, and could open the way to personalized therapies based on changing the vaginal microbiota.
In addition, bacterial and viral co-infections seem to exacerbate dysbiosis and contribute cumulatively to infertility. Hence the interest in studies that include not only bacterial assessments, but also viral and fungal ones, to fully understand the role of the microbiota in infertility.
