The science

The word means “month”. Science still can’t say what a normal one looks like.

This page sets out what our work is based on: what is known about menstruation, what is missing, what others have done, and what we still have to find out. Every figure has a source and a label that says how sure we are.

VerifiedWe read the original source.
SourcedFrom a named source we have not fully checked.
EstimateOur own calculation or judgement.
PlanWhat we intend. Needs ethics approval and funding.
Not yet knownResearch still has to show it.
1 · Why we are here

Medicine knows less about women. About menstruation, least of all.

1977–1993
US drug guidance kept women who could become pregnant out of early tests of new medicines.
SourcedFDA guidelines 1977 and 1993, via Liu & Mager, Pharmacy Practice, 2016
2×
Women have side effects from medicines nearly twice as often as men.
VerifiedZucker & Prendergast, Biology of Sex Differences, 2020
½
In 2013 the US regulator halved the recommended dose of a common sleeping pill (zolpidem) for women, whose bodies clear it more slowly.
VerifiedUS FDA Drug Safety Communication, 2013
38%
Women were 38% of the people in heart and vascular drug trials from 2010 to 2017.
VerifiedJin et al., Circulation, 2020
<1%
Endometriosis, PMS, menopause and three other women’s conditions cause 14% of the women’s health gap, but got less than 1% of the research money for the 64 conditions studied (2019–2023).
VerifiedWorld Economic Forum, Blueprint to Close the Women’s Health Gap, 2025, p. 19
25%
Women spend 25% more of their lives in poor health than men. This is a modelled estimate.
VerifiedWorld Economic Forum and McKinsey Health Institute, 2024
7–9 years
In Austria, endometriosis is diagnosed on average seven to nine years after symptoms begin.
VerifiedFrauengesundheitsbericht 2022, p. 73 (German)
1.5%
Only about 1.5% of mammal species menstruate. Lab mice and rats do not, so most lab research can’t show how periods work.
VerifiedBellofiore et al., American Journal of Obstetrics and Gynecology, 2017
The World Economic Forum links the funding gap to the lack of “a clear understanding of what a ‘normal’ period is”.
VerifiedWorld Economic Forum, 2025, p. 19
Austria’s women’s health report says data on menstrual health „fehlen … zum Teil gänzlich“ (are partly missing altogether).
VerifiedFrauengesundheitsbericht 2022, p. 28 (German)
2 · What is missing

Menstrual fluid is a sample almost no one collects.

Every month it leaves the body and is thrown away. The little research there is shows it holds information an ordinary blood test does not.

More than blood
Menstrual fluid is a mix of blood and shed womb lining. On average about a third is blood, and the share varies a lot between women.
Living cells
It carries living cells from the womb lining and from the immune system. A blood test does not give these.
Its own signals
Its proteins and immune signals differ from those in ordinary blood. Three independent studies found this; each was small.
Renewed about 400 times
The womb lining sheds and rebuilds without scarring, about 400 times in a lifetime. No other adult tissue does this as routine.

What research does not have

  • Only one published study has followed menstrual fluid over several cycles: 11 healthy women, up to 5 cycles each.

    VerifiedWyatt et al., Human Reproduction, 2021

  • As far as we know, no one has published samples over several cycles from women with a disease, or samples collected before a diagnosis.

    VerifiedPeriod Foundation evidence review, 2026

  • There are no reference ranges for menstrual fluid: no agreed picture of what is normal, and how much it changes from cycle to cycle.

    SourcedPeriod Foundation evidence review, 2026
3 · What has been done

Others have started. We build on their work.

Research on menstrual fluid is growing fast, mostly in small studies. These are the ones that matter most for us.

Antwerp, Belgium
Isala LUNA
About 100 healthy women gave samples over 5 cycles in a row, with a different period product each cycle.
United Kingdom, 2026
CycleTrack
Dried samples on pad strips, 3 periods per woman, linked to long-running UK family studies.
New York, USA
ROSE
Has collected liquid menstrual fluid with living cells since 2013, with more than 3,700 women enrolled.
Worldwide
Endometriosis research
About 35 studies have looked for signs of endometriosis in menstrual fluid. None has yet been confirmed in a prospective study.
Reporting 2027–2029
Three validation studies
ROSE II, MultiMENDo and Diamens test endometriosis signals in 200 to 250 women each. One has a site in Vienna.
USA, 2023
A first cleared test
One test on menstrual blood is cleared by a regulator: HbA1c, a diabetes marker, measured on a pad strip.

What is still missing: a year of samples from the same women, every cycle, from women with and without symptoms. As far as we know, no one collects that.

4 · The first study

First, a baseline.

Before anyone can see what is unusual, we need to know what is usual, and how much it changes from one cycle to the next.

2027 Plan
Pre-study

About 30 women give samples over three cycles. We test the kit, the drop-off and the lab handling, then decide whether to go ahead.

2027–2028 Plan
Baseline study

200 women in Vienna give a sample from every period for a year. Each cycle, we compare liquid samples (menstrual cup) with dried samples (pad strip).

~1,800
samples from 200 women over 12 cycles
Estimate
70–80%
of monthly samples we expect back, based on similar studies
Estimate
12
cycles per woman: enough to see how each woman varies
Plan

What it can show

  • How much menstrual fluid varies from cycle to cycle, within one woman and between women.
  • How liquid and dried samples compare, so later studies can choose the simpler one.
  • Whether earlier findings on endometriosis hold up in new women.
  • Whether markers in the sample track measured blood loss.

What it cannot show

  • It is not a diagnostic test, and no woman gets personal results.
  • 200 women are not enough for formal reference ranges. That needs a larger group.

Still open

  • Approval by an independent ethics committee. In Austria both studies need one.
  • A partner lab and a lead scientist. No one is confirmed yet.
  • Funding. We are applying; nothing has been granted.
  • Partner pharmacies and clinics in Vienna.
  • The final study design. Our current proposal includes women with endometriosis, with heavy bleeding, with symptoms but no diagnosis, and without symptoms.
5 · Why a biobank

Why a biobank, not just one study.

One sample is a snapshot.

Many markers change from cycle to cycle. Averaging more cycles makes them reliable. For a noisy marker, our calculation gives:

1 sample
0.25
3 samples
0.50
12 samples
0.80
EstimatePeriod Foundation calculation (Spearman–Brown), with assumed inputs
The past can’t be collected later.
To learn what changes before a diagnosis, you need samples from before it. They only exist if someone started storing them years earlier.
Questions no one has asked yet.
Stored samples, given with consent, can answer questions researchers have not thought of today.
Our blood. Our data.
The samples are held by a non-profit association, not a company. Names are kept apart from samples. Researchers and companies can apply for access on terms decided with the women who give, and every woman can withdraw.
VerifiedAs far as we know, no one collects menstrual samples every month for a year, or pairs liquid and dried samples every cycle.
6 · Our vision

What a biobank could make possible.

The more women, and the more years, the more questions research can answer. These are our estimates of what each stage could show. None of it is promised: each stage depends on the one before.

Each dot is 100 women. Estimate

  1. Autumn 2026
    Set-up
    Pre-study in 2027: about 30 women, 3 cycles

    Whether the kit, the drop-off, the cooling and the living cells work. No biology yet.

  2. 2027–2028
    200 women × 1 year
    About 1,800 samples

    How menstrual fluid varies from cycle to cycle. How liquid and dried samples compare. Whether earlier endometriosis findings hold up.

  3. 2029–2031
    2,000 women × about 3 years
    About 6,000 woman-years

    Reference ranges by age and contraception. A shared resource for teams developing tests. The first few women with samples from before a diagnosis.

  4. 2031 and beyond
    5,000+ women × 5 to 10 years
    25,000 to 50,000 woman-years

    Dozens of women with samples from before an endometriosis diagnosis: enough for first real tests of early signals. How the cycle changes with age, through the menopause transition and with treatment.

Research areas and the scale they need

Area
What exists today
What it would take
What is normal
No reference ranges for menstrual fluid.
Formal reference ranges usually need about 120 women per group (for example by age or contraception). With several groups, that means roughly 1,000 to 2,000 women.
Estimate
Endometriosis: confirm earlier findings
Small studies only.
200 women (about 50 with endometriosis, 60 without) can detect a moderate-to-large difference.
Estimate
Endometriosis: early signs
No samples from before a diagnosis exist anywhere.
In one large US study, about 2 in 1,000 women a year were newly diagnosed. 5,000 women over 10 years would give about 100 women with earlier samples.
Missmer et al., American Journal of Epidemiology, 2004
Estimate
Heavy menstrual bleeding
Four small studies on menstrual fluid, at most 72 women.
Heavy bleeding is common, so cases build up quickly. 200 women can detect a modest link between markers and measured blood loss.
Estimate
Menopause transition
No study of menstrual fluid.
Women from about 40, followed for years: the 5,000+ stage.
Estimate
Fertility, adenomyosis, effects of medicines
Very little or no data.
Later study groups. The scale is not yet known.
Not yet known

Rare diseases, such as cancers, would need tens of thousands of women. That is beyond our current plan.

7 · What we don’t know yet

What research still has to show.

These questions decide how well a menstrual biobank can work. We will report the answers, including the ones that go against us.

  • Not yet knownHow long living cells and RNA stay usable in a liquid sample on its way to the lab.
  • Not yet knownWhether frozen menstrual cells still work after thawing.
  • Not yet knownWhether markers in women with a disease are stable from cycle to cycle.
  • Not yet knownHow large the endometriosis differences really are. So far, one research group has measured them.
  • Not yet knownWhether women with endometriosis or heavy bleeding can use a cup for 12 cycles.
  • Not yet knownWhether cup and pad samples give different hormone results.
  • Not yet knownHow iron stores measured in menstrual fluid compare with a blood test.

We will publish what we find, including what doesn’t work.

This page grows with the research. Spotted an error, or know a study we missed? Write to us at hello@period.foundation.

Count me inSee the roadmap

Last updated: 4 October 2026