A new study reveals that the bacterial composition of a woman’s reproductive tract fluctuates with the menstrual cycle. Women with polycystic ovary syndrome (PCOS) lack certain bacteria previously linked to changes in metabolism. A researcher emphasises the importance of considering the menstrual cycle when investigating how bacterial composition affects PCOS.
About one in eight women worldwide have PCOS, a hormonal disorder with ovarian cysts and reduced fertility. This is frequently associated with obesity, leading to miscarriage and other pregnancy complications.
Researchers have long suspected an abnormal microbial composition in the reproductive tract of women with PCOS. This includes the upper part of the vagina near the uterine lining, which serves as the initial home for the fetus.
In a comprehensive study, researchers examined the bacterial composition in the vagina and on the uterine lining of women with PCOS, comparing it with that of women without PCOS across the menstrual cycle.
The findings offer deeper insight into how bacteria may affect infertility and hormonal imbalance related to PCOS and how these might be ameliorated in the future.
“We demonstrate that PCOS is not merely an infertility disorder but a complex hormonal disorder with multiple comorbidities. For women with PCOS, considering a broader range of challenges beyond fertility is crucial. Our results suggest potential in restoring a healthy bacterial composition in the reproductive tract to address PCOS-related issues, but further exploration is needed,” explains a researcher behind the study, Terhi Piltonen, Professor and Consultant, Department of Obstetrics and Gynaecology, Oulu University Hospital, Finland.
The research has been published in Human Reproduction.
Extensive investigation
Terhi Piltonen explains that numerous previous studies have explored the bacterial composition of the reproductive tract of women with PCOS. However, these studies often lacked quality. They failed to account for variation in bacterial composition at various sites within the reproductive tract and at various times in the menstrual cycle. In addition, they frequently included women who were not matched for body-mass index (BMI) or age.
In the new study, the researchers aimed to address these shortcomings by comprehensively analysing bacterial composition in various places in the reproductive tract of women with PCOS. They also adjusted for numerous factors, including age, BMI and menstrual cycle timing.
The research involved 52 women diagnosed with PCOS and 37 healthy controls. Researchers collected samples from the vagina and uterine lining before, during and multiple times after ovulation.
The bacterial composition was then compared between women with PCOS and healthy controls and across the phases of each woman’s menstrual cycle.
“Different phases of a woman’s menstrual cycle are associated with varying hormone concentrations, which can influence bacterial composition. Investigating these differences at various times during the menstrual cycle was therefore crucial,” says Terhi Piltonen.
Menstrual cycle has the greatest effect
The results demonstrated that the menstrual cycle causes the greatest difference in bacterial composition within a woman’s reproductive tract.
This means that, at certain times in the menstrual cycle, many bacteria of certain species are present in the reproductive tract near the uterine lining; at other times, different bacteria dominate.
According to Terhi Piltonen, previous research suggests variation between women with and without PCOS. However, this new study found only slight differences.
The researchers found that women with PCOS exhibited changes in bacteria related to metabolism and the uterine environment, but only for two types of bacteria.
Women with PCOS had fewer of these two bacteria, and they may play a crucial role in the fetal environment during early pregnancy, when women with PCOS often experience miscarriage.
“With our study, we adjusted for menstrual cycle variation, age and BMI, enabling us to determine the real differences between women with and without PCOS,” explains Terhi Piltonen.
Complex interaction
Terhi Piltonen explains that the study helps researchers to understand the complex interaction between PCOS, the menstrual cycle, hormones, bacteria and metabolism.
Previous studies by the same research group examined changes in gut bacteria composition among women with PCOS and those experiencing mental stress.
These studies highlighted that PCOS and mental stress could lead to alterations in gut bacterial composition, which were linked to changes in the body’s glucose metabolism.
As a result, women with PCOS showed higher insulin resistance, even at the same BMI.
“Our new study shows that there are specific changes in the bacterial composition of the reproductive tract of women with PCOS. Most of these changes are related to the menstrual cycle and only some milder changes were related to PCOS status and related metabolic effects. Controlling BMI and age eliminated most of the differences between PCOS and controls. This highlights the need to consider these factors when investigating the effects of altered bacterial composition in the reproductive tract of women with PCOS. Future research may help to determine whether altering the bacterial composition might address some of the problems women with PCOS often face, such as miscarriage or other pregnancy complications,” concludes Terhi Piltonen.
