In the same way that everyone has a unique gut microbiome, every woman has their own unique community of vaginal microbes. This is your vaginal community state type or CST. What makes up this vaginal community can fluctuate depending on various factors, such as antibiotic use, pregnancy, and how often you have sex.
Vaginal microbiome communities can be broadly clustered into five main types, depending on species composition [1], [2].
How CSTs are organized
CST 1, 2, 3, and 5 are all dominated by a single Lactobacillus species, which helps to protect the vaginal terrain and keeps infection at bay. This is a good thing.
On the other hand, CST 4 may be disruptive and linked to issues like:
- Bacterial vaginosis
- Aerobic vaginitis
- Urinary tract infections
- Group B Strep
- Infertility
- Preterm birth
CST 4 can be subdivided into three smaller subtypes, and 4-C can be further broken down into five additional subtypes.
Five vaginal community state types (CSTs)
CST 1
Type 1 vaginal community is one of the most common among women, especially in White and Asian women.
Compared to other CSTs, type 1 is dominated by Lactobacillus crispatus and has the lowest pH (under or equal to 4.5) [3]. This low pH creates an acidic environment that makes it hard for disruptive microbes to thrive.
Pregnant women with this type of vaginal community are at lower risk of preterm delivery [4], [5].
CST 2
While type 2 vaginal community is not very common, it’s still associated with wellness. Type 2 is dominated by Lactobacillus gasseri. Compared to other CSTs, it has a protective, lower pH of 4.5 to 5.5 [1], [2].
This vaginal community is very stable over time and is associated with a lower risk for both sexually transmitted infections [6], [7] and preterm delivery during pregnancy [4].
CST 3
The type 3 vaginal community is one of the most common and is dominated by Lactobacillus iners. The pH is protective and typically under or equal to 4.5 but still slightly less acidic than CST 1 [1], [2].
Although considered healthy, the type 3 vaginal community is less stable over time and could mean an altered microbiome [9].
CST 4
Type 4 vaginal communities are not dominated by Lactobacillus. Instead, they’re characterized by high species diversity and a less acidic (less protective) pH. But certain interventions can help CST4.
We know that subtypes 4-A, 4-B, and 4-C0 have a high pH ranging from 5.0 to 5.5 and that they’re associated with:
- Bacterial vaginosis [10]–[12]
- Infertility [13]
- Increased risk of preterm birth [14], [15]
This is because low levels of protective lactobacilli make these CST 4 subtypes unstable and more likely to harbor harmful microbes [16].
CST 4-A
Subtype 4-A, in particular, has a high abundance of Candidatus Lachnocurva vaginae (also known as BVAB1), and a moderate abundance of Gardnerella vaginalis, Atopobium vaginae, and Prevotella species. Both G. vaginalis and A. vaginae have been linked to preterm birth during pregnancy. And perhaps unsurprisingly, these species are considered pro-inflammatory. What’s more, both play a role in the development of bacterial vaginosis (BV), a condition marked by bacterial overgrowth, odor, and vaginal itching.
CST 4-B
Subtype 4-B has a high abundance of Gardnerella vaginalis and a moderate abundance of Candidatus Lachnocurva vaginae (also known as BVAB1), Atopobium vaginale and Prevotella species. When G. vaginalis teams up with other disruptive bacteria, you’ve got the perfect storm for bacterial vaginosis [1], [2].
CST 4-C
Subtype 4-C0 has a moderate amount of Prevotella. Certain species, such as Prevotella bivia, are associated with bacterial vaginosis and pelvic inflammatory disease. Subtype 4-C1 has a high abundance of Streptococcus species, which produce lactic acid that helps to lower vaginal pH and prevent pathogen invasion [1], [2]. If you are pregnant, however, Streptococcus agalactiae (Group B Strep or GBS) is of particular importance because this species can cause serious infections in newborns if passed on to the baby [17].
Subtype 4-C2 has a high abundance of Enterococcus species, which have been associated with aerobic vaginitis [18], [19] and urinary tract infections [20].
On the other hand, subtype 4-C3 has a high level of Bifidobacterium species, which produce lactic acid and lower the vaginal pH, protecting against pathogen invasion [21]. If you’ve ever purchased a baby probiotic, you may have run across bifidobacteria. These species are among the first bacteria to colonize the newborn gut. They are beneficial bacteria that support immune development and protect against infection [22].
Subtype 4-C4 has a high abundance of Staphylococcus species. Like CST 4-C2, this subtype has been associated with aerobic vaginitis [18], [19], [23].
CST 5
Type 5 is quite rare but associated with wellness. This CST is dominated by Lactobacillus jensenii, which helps maintain a low vaginal pH and protect against vaginal infections [24]–[26]. Pregnant women with this type of community have been shown to have a lower risk of preterm delivery [21].
CST Other
Some vaginal community types fall under the umbrella of "other" because they don't neatly fit into any of the main vaginal communities described so far. This is not necessarily a bad thing. Each vaginal community is unique. There may be other women in the world with a similar community, waiting to be discovered.
A community dominated by a species such as Lactobacillus johnsonii may be healthy, as high abundances of these bacteria are associated with good vaginal health and protection against vaginal infections.
If a vaginal community is dominated by a Lactobacillus species but other disruptive bacteria are also present, taking probiotics may help shift the vaginal community to a more favorable state and protect against infection or inflammation.
If you’re not sure about a particular species, the amount of each bacteria provided in our reports is key to figuring out whether intervention is needed.
As we continue to collect more data, our researchers may be able to categorize additional new vaginal community state types.
Why does CST matter?
Your CST matters because the composition of a vaginal community can fluctuate for a variety of reasons. This includes pregnancy or the postpartum period, as well as supplementation, menstruation, menopause, and antibiotic treatment [16].
Understanding your current CST can help you take action. If our reports show a disrupted vaginal community, you’re one step closer to identifying the root cause of any symptoms you might have - like vaginitis, bacterial vaginosis, or recurring urinary tract infections.
Community state types are also relevant to fertility and pregnancy. If your sampling results reveal a CST 4 during pregnancy, resampling prior to delivery and/or postpartum may be beneficial.
Likewise, if you have a disrupted vaginal community after giving birth and you plan on having another baby, waiting until your vaginal microbiome has returned to baseline may improve the odds of a healthy pregnancy, but additional research is required to confirm this hypothesis.
