Menstruation Is an Afterthought in Research. Here’s Why That Needs To Change

Women’s bodies are viewed as an inconvenience in research—especially when it comes to our periods.

Historically, women have gotten the short end of the stick when it comes to medical research, which has led to a lack of research and data on menstruation. (Pablo Blazquez Dominguez / Getty Images)

While working in a neuroscience lab prior to medical school, I took pride in the fact that the research I worked on included female mice and diligently analyzed sex differences. Historically, women have been neglected from research, largely due to the unsubstantiated belief that the female hormone cycle would cause variability in results. But these inequities weren’t just seen in rodent research—they were prevalent in human studies too. 

It wasn’t until 2016 that the NIH mandated the Sex as a Biological Variable (SABV) policy, which requires that SABV is factored into the experimental design of vertebrate animal and human studies. Only 20 years prior, in 1993, Congress mandated that women be included in clinical research studies. These policies suggest that great strides are being made in research toward sex and gender equity, right? 

Well, although it is mandatory to include female participants in clinical studies, one major aspect of women’s health is often omitted: menstruation.

On Sept. 27, 2022, the NIH published an article officially confirming a link between the COVID-19 vaccination and a temporary increase in menstrual cycle length. Although female participants were included in the COVID-19 vaccination trials, data was not collected from them regarding menstruation. It was only after the fact, when women began voicing lengthened periods and heavier bleeding online and to their doctors, that the impact of the vaccine on menstruation was studied. 

The lack of initial data on menstruation led to widespread misinformation being spread regarding the COVID-19 vaccine and infertility, impacting vaccine hesitancy. While these rumors were ultimately disproved, menstruation undoubtedly plays a major role in patients’ everyday health and lives. Menstrual changes have been reported by recipients of other vaccines as well, such as hepatitis B, typhoid and human papillomavirus (HPV). This begs the question: Why is menstruation being studied retrospectively, rather than prospectively, in clinical trials? 

Perhaps one answer could be that it’s difficult to monitor changes in one’s menstrual cycle. But that’s simply not the case. Numerous measurement tools exist to evaluate menstrual bleeding and symptoms. The Pictorial Bleeding Assessment Chart involves the participant using a chart to record the number of pads or tampons used each day. Another measurement tool, the Aberdeen Menorrhagia Severity Scale, assesses bleeding symptoms and quality of life as it relates to pain, symptoms, work life and activities.

Implementing these tools is as simple as adding a few more questions to the extensive questionnaires participants are already filling out. The real problem here is that female bodies, especially as it relates to menstruation, are viewed as an inconvenience in research. The changes in hormones and symptoms throughout the menstrual cycle have often been thought of as a confounding variable, which is what initially excluded female models from research for so long. 

Regardless, we’ve already accomplished mandating that female participants be included in research. So why can’t we stop there? What is so important about menstruation anyway? 

Broadly, the menstrual cycle is used as an indicator for women’s overall health. Physicians have even recently grouped the menstrual cycle in with body temperature, heart rate, respiratory rate and blood pressure as the “fifth vital sign.” Changes or irregularities in one’s menstrual cycle may indicate disease, infection or hormone imbalance, which may be impacted by lifestyle changes, stress, medication and more. While not always, irregularities in one’s menstrual cycle can also point to issues with fertility.

The status of one’s menstrual cycle can indicate problems in not only their reproductive health, but their mental and comprehensive physical health as well. 

Physicians have recently grouped the menstrual cycle in with body temperature, heart rate, respiratory rate and blood pressure as the ‘fifth vital sign.’

Over half of the world will experience menstruation at some point, yet data on menstruation is not routinely collected in vaccine trials. By neglecting to collect data on menstruation, researchers are potentially missing key indicators of women’s health that may influence the evaluation and usage of potential vaccines. It’s time to stop viewing female bodies, including the menstrual cycle, as an inconvenience, a confounding variable and a problem in clinical research. 

Of course, in order to make this change, we have some work to do.

As patients, we should question if and how menstruation was considered when taking new medications, vaccines and therapeutics.

As physicians, it’s imperative to assess clinical trials, dispel misinformation and improve health literacy by talking to patients about the impact a new therapeutic may have on menstruation.

Most importantly, as researchers, it’s crucial to include questions about menstruation in the clinical trials of all potential therapeutics, ensuring that research is conducted equitably and to completion. After all, menstruation is the “fifth vital sign” in the clinic. It’s time it becomes more than just an afterthought in the laboratory.

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Taytum Kahl is a medical student at the University of Chicago and is passionate about sex and gender equity in medicine. She previously worked as a COVID-19 vaccine health educator in a free clinic in Milwaukee and also conducted preclinical research on sex differences in long-term opioid withdrawal at Marquette University. She currently serves as a board member for the Maria Shelter Free Clinic, which serves women experiencing homelessness.