There is no doubt that our gut microbiota, the populations of mainly bacteria, have an impact upon our ability to get and stay pregnant. We talk so much about our gut microbiota, but now it is time to find out more about another important ecosystem in our body: our reproductive tract microbiota.
The Vaginal and Uterine Microbiota
A healthy vaginal microbiome is associated with an increased chance of conceiving and successful pregnancy. So what does a healthy vaginal microbiome look like?
The microbiota of a healthy, non-pregnant woman contains a variety of Lactobacillus species. These bacteria are thought to provide a healthy supportive environment that is conducive to conception.
The Lactobacillus bacteria produce lactic acid to maintain the pH of their environment and they dominate the microbiota of the vagina protecting it from harmful intruders. Lactobacillus love to use glycogen for energy and once they metabolise glycogen to glucose and maltose it is then further broken down to lactic acid. Lactic acid decreases the pH of the vagina to around 3.8-4.4 which creates a protective environment against the growth of pathogenic bacteria. This is one way that the body prepares for the impending pregnancy. Lactobacillus are very important in maintaining the pH of the vagina and consequently its microenvironment.
Some of the main bacteria in the vagina are L. crispatus, L. gasseri, L. iners and L. jensenii. Other bacteria that could cause a problem in the vagina if Lactobacillus are overrun include Gardenella, Atopobium, Mobiluncus, Prevotella, Streptococcus and Ureaplasm (just to name a few). The good news is that with a healthy level of Lactobacillus, these bacteria remain almost inactive or dormant.
Unlike the gut microbiome where diversity is key, in the vagina you want to have the genus Lactobacillus dominating. Lactobacillus know their job and are very protective of their environment. If Lactobacillus are threatened, they have the ability to promote antimicrobial defences which would kill other microbes that don’t belong. They are great at protecting and defending their territory.
Our Reproductive Tract Microbiota Impacts Pregnancy Success
Contraception, ovarian stimulation and hormone manipulation can have an effect on the health of the vaginal microbiome. These mostly decrease the number and types of Lactobacillus species in the vaginal microbiome and can cause an increase in bacteria such as Escherichia coli and Gardnerella both of which can be detrimental to the conception process as they cause infection.
There is a link between the success of assisted reproductive treatments and the health of the vaginal microbiota . Lower abundance of Lactobacillus, and higher abundance of pathogens Gardnerella and Prevotella are identified in women that do not fall pregnant following IVF, compared to those that have pregnancy success .
In 130 women undergoing IVF at a Danish Clinic, an abnormal vaginal microbiota was found in 28% of women. ‘Abnormal’ was categroised by the presence of high levels of Gardnerella vaginalis and/or Atopobium vaginae. Following IVF, women with a normal vaginal microbiota had a pregnancy rate of 35% while those with an abnormal microbiota had rates of only 9% . Almost half (45%) of women experiencing repeated implantation failure have a non-Lactobacillus dominant endometrial microbiota  .
Early and late miscarriages have also been linked to the composition of the vaginal microflora. A lower abundance of Lactobacillus , and an increasing presence of Mollicutes have been found in the vaginal microflora of women experiencing preterm premature rupture of membranes . Microbial disturbances such as bacterial vaginosis have also been associated with preterm birth .
Our reproductive tract microbiomes impact the chance of conception, and healthy pregnancy progression so nurturing this is important for positive pregnancy outcomes.
What’s the Gut- Reproductive Tract Connection?
While our gut and reproductive organs may seem far apart, what happens in our gut can influence what goes on in our reproductive organ ecosystem. Bacteria have been shown to ascend from the rectum to the vagina and diet which manipulates the gut microbiota can be an effective treatment strategy for bacterial vaginosis .
Composition dynamics of the vaginal microbiome are influenced by changing levels of sex hormones which can be regulated by our gut. The health of our immune system, psychological stress, antibiotics and smoking all play a role in shaping the diversity of our gut microbiota but these are also linked to the health of our vaginal microbiota .
The gut and female reproductive tract are in constant communication with each other via microbial metabolites, our immune system and our circulatory system .
Studies exploring the gut microbiome and vaginal microbiome in the same population are few, but those in women with endometriosis show that where gut dysbiosis exists, vaginal dysbiosis is present . reduced . Nurturing our gut health is connected to the health of our reproductive tract. Compounds that increase the diversity of our gut microbiota have been shown to boost Lactobacillus abundance in the vaginal microbiota.
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