The role of vaginal bacterial flora in fertility

The protective role of a woman’s vaginal microbiota has become increasingly evident over the years, as researchers have successfully linked bacterial flora imbalances with a range of medical conditions ranging from bacterial vaginosis to urinary tract infections,

The importance of the vaginal bacterial flora and the understanding of the complex balance that allows protection from infections has been the subject of studies and research for some time. Recently, however, researchers have begun to turn their attention to the role that the vaginal microbiota plays in women’s fertility.

In women undergoing IVF treatment, pregnancy rates are much lower when women have an imbalance in their vaginal bacterial flora.

Is it possible to correct this problem and increase the pregnancy rate of these women? To find out, five Danish fertility clinics, in collaboration with Statens Serum Institute and Osel Inc. have started a new randomized study. The aim is to understand whether a specific probiotic can be used to restore an optimal vaginal microbiota, and therefore increase the possibility that a woman struggling with infertility can become pregnant.

High levels of two specific vaginal bacteria (Atopobium vaginae and Gardnerella vaginalis) are diagnostic markers of an abnormal vaginal microbiota that could lead to compromised implantation and subsequent poor reproductive outcome.

The premises of the study are based largely on previous research, published in 2016 in the journal Human Reproduction, which found that only 9% of Danish women undergoing in vitro fertilization (IVF) with abnormal vaginal microbiota, became pregnant against the 44% of those with a better balance of vaginal bacterial flora.

Approximately 20% of all women undergoing fertility treatment have an abnormal vaginal microbiota which may also reside in the upper reproductive tract, i.e. the uterus and fallopian tubes. Unfortunately, many of these women have no symptoms, so this problem goes unrecognized.

The new study in progress

The study will focus on 333 women, with abnormal microbiota, undergoing treatment for infertility.

The 333 women will be randomized into three groups: one group will receive no treatment, the second will receive antibiotics only, and the third will receive antibiotics plus a vaginal probiotic that contains the bacterium Lactobacillus crispatus. The probiotic product, called Lactin-V, has already been tested in other clinical trials against bacterial vaginosis and recurrent urinary tract infections.

The active ingredient in Lactin-V is Lactobacillus crispatus CTV-5, a naturally occurring strain isolated from the vagina of a healthy woman. The strain is grown by fermentation, dried by freeze-drying and ground into a powder. The powder containing the live bacteria is administered through special devices by the vaginal route.

The study aims to monitor the pregnancy rates in the three groups and the differences in order to understand the effectiveness of the probiotic.

What is the optimal bacterial flora (microbiota) and what is its role?

The protective role of a woman’s vaginal microbiota has become increasingly evident over the years, as researchers have successfully linked bacterial flora imbalances with a range of medical conditions ranging from bacterial vaginosis to urinary tract infections, sexually transmitted such as HIV.

The bacteria that produce lactic acid, and in particular various species of Lactobacillus, are classified among the “good bacteria”, i.e. those that provide protective help, probably through various mechanisms, including ecological competition with potentially harmful bacteria and the lowering of Vaginal pH thanks to the production of lactic acid.

Researchers are trying to figure out what the optimal balance is and how to restore it.

We conducted a phylogenetic analysis of the vaginal microbiota of 396 North American women who were of reproductive age and represented different racial/ethnic groups (White, Black, Hispanic, and Asian). 4 dominant bacterial species were found: Lactobacillus iners, L. crispatus, L. gasseri and L. jensenii. However, their relative proportion varied among the racial/ethnic groups studied.

Despite the differences, it has been seen that the presence of Lactobacillus is a positive factor and that Lactobacillus crispatus is particularly important for a good bacterial flora. Lactobacillus crispatus, based on the data available to researchers, is probably the best for optimal vaginal flora, because it is associated with the lowest risk of most infections.

Restore balance

Even if an optimal vaginal microbiota environment can be restored, for example by introducing L. crispatus through Lactin-V, this does not mean that long-term colonization can be achieved.

A number of situations, including menstruation or sexual activity, have the potential to alter a woman’s microbiota.

One of the next objectives will be to understand how to maintain an optimal vaginal flora for a long time to reduce the risk of recurrence of infections. And then understand if this optimal flora can have benefits not only against infections but also for women’s fertility.

The Danish study that has just begun, and which will be completed within a couple of years, will be able to provide some answers and we will keep you updated.

Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.

Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.

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