Until very recently, it was assumed that the uterus was a sterile environment – that is, until the advent of next-generation gene sequencing that revealed the presence of an ‘endometrial microbiome’ containing bacteria. In general, most healthy women (without any complaints of vaginal symptoms) have a uterine microbiome that is dominated by Lactobacillus species; it is entirely possible, however, to have a microbiome that is comprised of other bacteria and still not has any symptoms.
Researchers believe that the presence of these healthy, commensal, bacteria helps prevent against bacterial vaginosis and other uterine gynecological diseases/infections by lowering the pH of the uterine (and vaginal) environment. We’ve known for a long time in the naturopathic realm that promoting healthy pH and bacterial populations in the vagina is necessary to prevent and treat bacterial infections, so it makes sense that this is also happening in the uterus (which is, by the way, connected to the vagina through the cervix which is not airtight for obvious reasons).
What’s really novel and interesting about the fact that there are bacteria in the uterus, is that there have been reports emerging that suggest that the human uterine microbiome may be related to implantation success during an IVF cycle.
In this study from 2016, researchers looked at a small group of women undergoing IVF and divided them into two groups after testing vaginal and endometrial aspirates for their bacterial DNA. They then compared the groups by IVF outcome to see if their endometrial microbiome affected the outcome of their IVF cycles.
Turns out it did. The two groups they created were: 1. women who had a Lactobacillus dominant microbiome (LDM) had >90% Lactobacillus species, and 2. those who had a non-Lactobacillus dominant microbiome (NLDM) were at <90% Lactobacillus species, or >10% other bacterial species.
They found that the women in the NLDM group had significantly lower implantation, pregnancy, ongoing pregnancy, and live birth rates.
Now, this study didn’t look at women with any intervention – ie. they didn’t treat the NLDM group and no one was taking any probiotics or antibiotics during the trial. More recent studies have trialed some interventions in NLDM groups (ie. antibiotics, oral probiotics, and vaginal probiotics), and the outcomes have been positive, but not quite as striking as that first study. In a follow-up study, for example, they found that at least 80% Lactobacillus dominance may be enough for embryo implantation, and suggested that another species of commensal bacteria (Bifidobacteria) may also be acceptable for implantation. So we’re nowhere near 100% certainty of the exact makeup of the microbiome that is necessary to support implantation, but we know enough to say that it likely does play a role.
These studies give us reason to pause and to believe that the type of bacteria present in the uterus may be playing a role in IVF success. What we know for sure, is that supporting a healthy microbiome in your system prior to IVF transfer day is very likely not going to be detrimental to your IVF success. It may even help support a positive outcome!
At Acubalance, we use a vaginal probiotic suppository protocol for patients leading up to frozen embryo transfer, as a first step to support a healthy vaginal and endometrial microbiome. While most vaginal probiotic products are Lactobacillus species dominant, there is one product in particular that I like for the particular strains of Lactobacillus, and the number of species per ovule.
If you are preparing for a FET in the near future and are a patient of Acubalance you can pick up your bottle of probiotics we specifically carry to improve your FET success.