Very little is known about the link between endometriosis and the vaginal microbiome, but one thing is for sure: they’re two severely misunderstood and under-researched — albeit emerging — areas of female reproductive health. You can blame the gender health gap for that.
But is there a relationship between the vaginal microbiome and endometriosis? Some recent research seems to suggest that there is, but we don’t have a definitive answer yet. Below, we look at how endometriosis and the vaginal microbiome may be linked, and what it could mean for women’s health.
What is endometriosis?
Endometriosis is a chronic condition that affects 10% of reproductive-aged women — but it could be more because it’s really hard to diagnose. Endometriosis happens when tissue similar to the lining of the uterus (endometrium) grows outside of the uterus - such as the ovaries, fallopian tubes, and sometimes bowels.
These growths, also known as lesions and implants, mimic the endometrium by responding to hormonal changes during the menstrual cycle. They thicken and shed every month, but because they’re trapped they have nowhere to go (unlike your period, which sheds via the cervix and vagina). This is what causes pain and inflammation.
Symptoms of endometriosis
The most common symptoms of endometriosis are:
- Painful periods (dysmenorrhea)
- Pelvic pain
- Heavy periods
- Pain when having sex or going to the bathroom
- Infertility or difficulty conceiving
- Diarrhea, constipation, bloating, or nausea.
Symptoms of endometriosis can vary greatly from person to person, so you might experience just some or all of these symptoms. For some people, symptoms might not even be that noticeable, but for others, the condition can be debilitating — that's part of the reason why endometriosis is so hard to diagnose.
How is endometriosis diagnosed?
Getting diagnosed with endometriosis may take some time because the exact cause is still unknown and symptoms vary so much, often overlapping with other reproductive health disorders.
It can take as long as 8-12 years to get a diagnosis (sometimes longer). To make matters worse, painful periods are often considered normal, so many people don't realize they should see a doctor, who may straight up dismiss their pain.
The most common way of diagnosing endometriosis is laparoscopic surgery (or a laparoscopy). This is where a surgeon passes a thin tube through a small incision in your tummy (known as keyhole surgery) so they can use a camera to look for any endometriosis lesions. If any lesions are found, the surgeon might remove them during the laparoscopy.
Although it’s considered a “minimally invasive” surgery, let’s face it, it’s still pretty invasive. Thankfully, new techniques are being developed to find lesions in a less invasive way, such as with ultrasound.
Endometriosis is classified into three types, based on where the endometrial tissue is found:
- Superficial peritoneal endometriosis (SPE). This type is the least severe and causes mild pain. In SPE, the endometrial tissue sticks to the peritoneum, which is the membrane that lines the inside of your abdomen and pelvis.
- Ovarian endometrioma (OMA). Ovarian endometriomas, or “chocolate cysts,” are sacs filled with dark fluid, commonly found in the ovaries. OMA is associated with severe pain, but 25% of women with ovarian endometriomas can be pain-free.
- Deep infiltrating endometriosis (DIE or DI). In this particular type of endometriosis, the tissue of the uterus can spread to other organs like the bowels, bladder, rectum, and ovaries. Although it's not a common occurrence, sometimes organs can become stuck together due to a significant amount of scar tissue — a phenomenon known as a "frozen pelvis". This is the most severe form of endometriosis, and only around 5% of women are pain-free.
There is also a fourth, very rare type of endometriosis where lesions are found outside the pelvic region, on the abdominal wall. In some cases, the endometrial cells can also attach to scar tissue from previous surgery, such as a C-section.
What causes endometriosis?
That’s the million-dollar question. The cause of endometriosis is unknown, but scientists have several theories as to why it may develop.,
- Retrograde menstruation. This is when menstrual blood flows backward through the fallopian tubes and ends up in the abdominal cavity. This can cause endometrial cells to implant in other tissues and grow. It's important to note that this can happen even with completely intact and healthy anatomy because there is a gap between the fallopian tube and ovary (yep, they're not attached). While retrograde menstruation is believed to be quite common and happens to most women at some point in their lives, the idea that retrograde menstruation is the main cause of endometriosis is being questioned by scientists due to a lack of evidence.
- Cellular mutation (aka “metaplasia”). This happens when a cell changes from one form to another. So endometriosis would happen when cells outside the uterus change into endometrial cells and start to grow.
- Stem cell theory. This theory suggests that stem cells from the uterus can travel outside of the uterus and create tissue similar to the endometrium, which can then develop into endometriosis lesions.
Experts are leaning toward the last two potential causes of endometriosis because most endometrial lesion cells are clonal, which means they all came from one single progenitor cell — this is a type of biological cell that can differentiate into a specific cell type. Each time a cell replicates, it has the potential to mutate and cause issues.
Since endometrial cells can grow the fastest, they also have a higher risk of mutation. When these cells grow in the wrong place, it can cause endometriosis lesions. The main cause of this still isn't clear, but it could be due to changes in our DNA or changes in what genes are expressed.
Factors like toxins or immune stimulation can also cause these changes and mutations, which could explain why some women are more prone to endometriosis if they have a history of vaginal infections, pelvic inflammatory disease (PID), or human papillomavirus (HPV.)
One recent study seems to back this theory. The research analyzed a large dataset of human genomes (a complete set of DNA) and found 49 different genetic markers associated with endometriosis. Another paper found that the expression of five human genes in the endometrium was linked to endometriosis. These are very promising studies that could lead to future human genetic testing for endometriosis, but it’s only the start.
Talk of mutations and diseases can make it sound scary, as though endometriosis was similar to cancer. It's natural to feel worried, but it's important to know that there is a difference between endometriosis and cancer because endometriosis is considered a non-cancerous or "benign" disease.
Treatment for endometriosis
Unfortunately, there is no cure for endometriosis (yet) but there are treatments that can help manage symptoms.
Doctors usually suggest using hormonal birth control like the pill, and nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen to help manage heavy and painful periods.
If this helps, they might want to confirm the diagnosis with a laparoscopy and potentially remove any lesions. However, it's important to know that symptoms can come back even with pain management and surgical interventions.
Finally, the most “definitive” approach is to surgically remove the uterus (partial hysterectomy) and/or ovaries (total hysterectomy). If the endometriosis hasn’t affected the ovaries, then your doctor will recommend a partial hysterectomy, especially if you want to have children in the future via assisted reproductive technology (ART).
Is there a link between the vaginal microbiome and endometriosis?
The vaginal microbiome is linked with many gynecological conditions, from chronic vaginal infections and your risk of getting an STI, to infertility. So, could it be linked to endometriosis, too? Unfortunately, the science is unclear.
A recent systematic review compared seven different endometriosis microbiome studies. It found that the studies varied widely in how they sampled the microbiome (vagina, cervix, or endometrium) and the bacteria found. For example, some studies found that Atopobium was more frequently detected in the vagina of endometriosis patients while other studies found it more frequently in patients without.
Additionally, the studies weren’t consistent in the way they even classified endometriosis to begin with. Some used a scoring system while others compared endometriosis and adenomyosis, a disorder similar to endometriosis that causes lesions within the uterine wall.
In most studies, the control population was made up of patients going in for “benign gynecological surgeries”. This is problematic because the reason for these surgeries is varied and it’s hard to determine if they’re an appropriate control population. Finally, most of the studies had a very small sample size.
New evidence published this year (that wasn’t involved in the systematic review) suggests that Fusobacterium bacteria might have a link with endometriosis. The study found Fusobacterium in over 60% of women with endometriosis, but only in 7% of women without endometriosis. The researchers also believe that antibiotics might be a good way to treat endometriosis. But, like we always say, correlation doesn't mean causation, so more research is needed to figure out exactly how endometriosis and dysbiosis are linked.
One thing we do know is that endometriosis isn’t associated with lower levels of lactobacilli, the good, protective bacteria that live in your vaginal microbiome. The MVPs of vaginal flora, if you will. Several studies found that Lactobacillus was the most common organism found in both endometriosis patients and control patients (Chen 2020, Ata 2019, Akiyama 2019, Hernandes 2020, Chao 2021, Perrotta 2020).
It’s still possible that the vaginal microbiome is connected to endometriosis, and while it’s an exciting theory that gets us one step closer to finding a cure for endometriosis, we just don’t have the studies to prove it yet. Thank you, gender health gap!