Women's reproductive organs are home to plenty of microorganisms, and identifying them may help us improve women's health.

Scientists have long known that the vagina is home to trillions of bacteria, but much less is known about the community of organisms inhabiting the rest of women’s reproductive tracts — from the uterus to the ovaries. In a study published today in Nature Communications, researchers in China identified the microorganisms found in six parts of the reproductive tracts of 110 women. The research can help scientists figure out what microbes and bacteria are found in healthy women, and which ones are associated with certain diseases.

Scientists are just starting to figure out how the microorganisms that live on and inside our body, called the microbiome, affect our health. Over the past decades, new genetic tools are giving researchers powerful new ways to study microbes sampled from our bodies, including our reproductive organs. Previous research has shown that certain bacteria found in vaginas, for instance, can make an anti-HIV vaginal cream less effective. Changes in vaginal microbes also play a role in sexually transmitted infections, as well as urinary tract infections.

To find out about the lesser-known communities of microorganisms beyond the vagina, researchers in China sampled the microbes found along the reproductive tracts in 110 women of reproductive age; they analyzed six sites, including the mucus that lines the inside of the uterus and the tubes that carry eggs from the ovary to the uterus, called fallopian tubes.

Consistent with previous research, the researchers found that certain parts of the vagina were dominated by Lactobacillus bacteria, the same family of friendly bacteria found in fermented foods like yogurt. The microbial community, however, was different in the other parts of the reproductive tract: the mucus lining in the inside of the uterus and the fallopian tubes had very little Lactobacillus, and many more bacteria belonging to a family called Pseudomonas. The researchers also found that bacterial communities varied based on menstruation, and even what phase of their periods women were in. They also found that certain bacteria were associated with certain diseases. For instance, women with benign tumors in the uterus had more of the bacterium Lactobacillus iners in their cervical mucus than women who didn’t have the tumor.

The study involved only 110 women in China, and it’s known that people in different countries have different microbiomes. Still, the findings could help scientists better understand what microbes and bacteria are associated with certain conditions, which could help when testing for diseases as well as when developing treatments.

The research also adds to evidence that babies don’t develop in sterile environments. Until fairly recently, a woman’s uterus and the pancake-shaped organ that provides nutrients to the baby, called the placenta, were believed to be germ-free to protect the baby. But research is beginning to challenge that view, showing, for instance, that the placenta is not sterile. Today’s study shows the rest adds to that, by identifying more organs where these microorganisms live.

The research is still early, and it’s hard to say exactly what role these microbes play in women’s health. So the next steps include determining how they interact with their host environment. Previous research into the microbiome in other areas of the body suggests the interactions between a person and their local bacteria can help regulate some bodily functions — and now it’s time to see if that’s true here, too.