Clinical pearls:
- Different
bacterial species were detected between vagina and endometrial cavity of
the same subjects.
- The
microbiota in the endometrial cavity is labelled as Lactobacillus-dominated
microbiota (>90% Lactobacillus spp.) or a non-Lactobacillus-dominated
microbiota (<90% Lactobacillus spp. with >10% of
other bacteria).
- The
composition of endometrial microbiome is not regulated by the hormonal
cycle and non-Lactobacillus-dominated microbiota during the
receptivity phase correlates with significant decrease in implantation,
on-going pregnancy, pregnancy and live birth rates.
It has been believed
since last 50 years that uterine cavity and endometrium is sterile and devoid
of microbial habitat in the absence of infection. The sterile womb paradigm was
coined by the French pediatrician Henry Tissier and postulated that human
infants develop in a sterile environment. [1]
Recent
advances in genomics and bioinformatics have led to identifying microbiota in many
body organs that were previously thought to be sterile by use of 16S rRNA
gene-based bacterial detection and identification techniques. By using this
newer advances in microbiology it has been proved that upper genital tract harbors
a distinct set of microbiome and is differs considerably in health and disease states.
A study
published in the December issue of American journal of Obstetrics and Gynecology (ACOG) by Moreno et al,[2]
not only demonstrated that endometrium harbors microbes and endometrial microbiome
has a lot in common with vaginal microbiome. The study further demonstrated that like
vaginal microbiome, the endometrial flora is also divided into Lactobacillus dominant
(LD) and non-Lactobacillus dominant (NLD) communities.
The
researchers obtained paired samples from vagina and endometrial cavity in 13
fertile women in both receptive and prereceptive phases of the same menstrual cycles.
(n=52). To study the hormonal influence on endometrial microbiome during the preparation
of endometrium for implantation samples of endometrial aspirate collected from 22
fertile women.
Finally, to
study the impact of altered endometrial microbiome on reproduction, the endometrial
aspirate was assessed by implantation, miscarriage, ongoing pregnancy, and
live birth rates in 35 infertile women undergoing IVF by endometrial
receptivity array (ERA).
The study results
showed that:
Different bacterial
species were detected between vagina and endometrial cavity of the same
subjects.
The
microbiota in the endometrial cavity is labelled as Lactobacillus-dominated
microbiota (>90% Lactobacillus spp.) or a non-Lactobacillus-dominated
microbiota (<90% Lactobacillus spp. with >10% of other
bacteria).
The composition
of endometrial microbiome is not regulated by the hormonal cycle and non-Lactobacillus-dominated
microbiota during the receptivity phase correlates with significant decrease in
implantation, on-going pregnancy, pregnancy and live birth rates.
This pilot study
has opened the doors for many basic, translational and clinical studies in
future. It has also drawn our attention to the fact that reproductive success
does not solely rely on endometrial histology and gene expression.
Linda C.
Giudice, MD, PhD, Distinguished Professor and reproductive endocrinologist at
the University of California San Francisco said in an accompanying editorial “The
ongoing revolution in technology, science, multiple omics, and multidimensional
data analysis has opened the window of implantation to a greater level of
scrutiny. It is time to further investigate the endometrial microbiome and
expand research to its virome, fungome, epigenome, and metabolome to increase
our understanding the biology of this dynamic tissue and to develop targeted
therapies of endometrial disorders that underlie infertility and poor pregnancy
outcomes and affect women’s health more broadly. We are indeed on the threshold
to transform clinical reproductive medicine and improve reproductive outcomes
with precision and personalization for individual patients.”
[2] Moreno,
I., Codoñer, F.M., Vilella, F. et al. Evidence that the endometrial
microbiota has an effect on implantation success or failure. Am J
Obstet Gynecol. 2016; 215: 684–703
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