Vaginal microbiota: more lactobacilli, fewer miscarriages?

Miscarriage: Every pregnant woman’s nightmare.1 in 5 pregnancies end before 12 weeks due to early miscarriage. Half of these are linked with chromosomal abnormalities (genetic errors). Late miscarriages can still occur between 12 and 24 weeks, and 2 in 3 cases are caused by an infection. However, vaginal microbiota bacteria could prove to be precious allies in preventing miscarriage.

Long live lactobacilli!

Let’s get one thing straight from the start: vaginal microbiota like to do things differently. Unlike other body flora, which benefit from diversity, the vagina is quite monomaniacal; good vaginal health is believed to be closely associated with a very low diversity and high proportion of lactobacilli. Very, very high in fact: in a recent study, these bacteria, recognized easily by their rod shape, accounted for 94.2% of the vaginal flora bacteria in ¾ of the 167 pregnant women monitored... But what about the other women? Their lactobacilli made up only a small percentage of their microbiota, i.e., 18.5% of their vaginal bacteria. Yet this decrease in lactobacillus dominance appears to have serious consequences on pregnancy outcome.

_{Sources (sidenote: Why we need to talk about losing a baby_WHO )}

From vaginal microbiota to miscarriage

Miscarriages that have no genetic explanation are more common in women who have a vaginal microbiota that is:

• richer in bacteria and diversity
• low in lactobacilli (as has already been shown in a previous Chinese study)
• rich in other bacteria, for example streptococci (60% of cases) or Prevotella (40% of cases).

Moreover, this decrease in lactobacillus dominance appears to be associated with more frequent vaginal inflammation. Therefore, it would appear that a lower concentration of lactobacilli goes hand in hand with inflammation of the female reproductive system. As a direct consequence, this creates an environment unfavorable for fetus implantation, and the pregnancy cannot progress normally. This would explain the higher frequency of miscarriages observed when lactobacilli have disappeared. Yet it also creates a glimmer of hope, as vaginal microbiota may be a target of choice for reducing the risk of miscarriage.