Here is our myth-busting guide to help you know the difference between ‘normal’ and problematic ‘heavy’ menstrual flow, estimate your own fluid/ blood loss, and find out which underlying conditions can cause Heavy Menstrual Bleeding (HMB).
1. How much blood/ fluid loss is ‘normal’?
First off, you need to know something that you were probably never taught at school (even medical school!)- Which is that only approx. 50% of menstrual fluid is blood .
On average, people who menstruate lose ~ 70-80 ml of fluid (~ 35-40 ml of blood ) per period . This amount of fluid would fill a double espresso cup (image on left) .
In fact, anything up to ~ 160-170 ml of fluid (~80 ml of blood) per period falls within the ‘normal’ range . This is because ~ 95% of all people who menstruate typically lose less than this amount . This total amount of fluid would fill a tall (7oz) disposible plastic cup (image on right) .
Notes– variation is the norm when it comes to menstrual health- it is important to track your cycle for a while to work out what is the ‘normal’ range of experiences for you. This will help you to spot any significant or unusual changes in the future. Hormonal contraceptive medication is known to significantly reduce cyclical fluid/ blood loss in those with no underlying health issue .
What’s not normal?
Technically speaking, Heavy Menstrual Bleeding (HMB) is losing over 80 ml blood (~ 160-170 ml of fluid) per period . Most people with this condition lose between 80- 200 ml of blood (160-400 ml of fluid) per period, but some people can lose even more than this .
Heavy Menstrual Bleeding (HMB) can also make the period last longer than a ‘normal’ one . Most people have periods that last between 3-7 days, with at least 80% of the total fluid/blood loss happening on days 1-3 . If your period typically lasts longer than 7 days, especially with significant fluid/ blood loss over more than just the first 3 days, you may be experiencing HMB .
Left untreated, HMB rapidly results in iron deficiency anaemia, and the awful thing is, anaemia makes periods even heavier … It’s a truly vicious cycle! It is therefore important for clinicians to simultaneously treat iron deficiency anaemia alongside any other investigations/ interventions for Heavy Menstrual Bleeding .
2. How do you measure menstrual blood/ fluid loss?
We can roughly calculate blood loss by simply halving the total fluid loss… So this really depends on the collection method you prefer to use.
Menstrual cups now provide the easiest and most accurate way to measure fluid levels, since many of them come with a handy scale on the inside . Others may just list their total capacity size, which still enables users to estimate how much fluid has been collected over the course of a period. Simply look at how much fluid is in the cup when changing it and note it on your phone, or on paper. Do this throughout the whole period, since diagnostic cut off points are based on total blood loss per period.
Disposable items, such as pads and tampons all have to meet the same absorbency standards . This means that it is possible to roughly estimate fluid loss by counting how many tampons or pads you bleed through during your period.
The chart below shows the exact standard ranges , which are actually based on weight, rather than fluid level- but this is still a good way to roughly calculate fluid loss. For example, each (fully soaked) regular soaked tampon or pad ~ 7ml, each ‘super’ ~ 10ml, each ‘super plus’ ~ 13ml, and each ‘ultra’ ~ 16ml.
The problem is that many people change their pads and tampons before they are fully soaked, so the accuracy of this method is reduced – although it is possible to use a visual ‘pictogram’ scale to estimate fluid loss . People also tend to use products with different levels of absorbency throughout their period, so it is important to note down the exact type of product used.
|Ranges of absorbency in grams||Corresponding term|
|6 and under||Light|
|6 to 9||Regular|
|9 to 12||Super|
|12 to 15||Super plus|
|15 to 18||Ultra|
Washable items, such as period pants, or washable pads may make estimating fluid loss more difficult, because there is no universal standard of absorbency for these items (yet). However, if you are concerned that you may be experiencing heavy bleeding, it might be worth using a cup for a few cycles, just to help you and your doctor make a more informed decision about possible treatment options?
Another less accurate, but practical guide is noting the number of times you have to change your menstrual underwear, cup, pad or tampon in a given time period. If you can answer yes to any of the following questions, you could well be experiencing Heavy Menstrual Bleeding (HMB) ;
- Do you have to wear tampons/ cups and towels together to prevent leaking through clothing?
- Do you have to change items more than once every 2 hours?
- Does blood ever soak right through your clothes, even though you are using a menstrual product?
- Do you have to stay off work or cancel social engagements due to heavy bleeding?
3. What causes Heavy Menstrual Bleeding?
Note– It is very important that you seek medical advice if you experience a significant change in your period flow, or any mid-cycle bleeding.
Heavy Menstrual Bleeding (HMB) can be caused by various, and sometimes multiple, factors . Luckily for us, the possible causes are listed in a handy acronym- PALM-COEIN .
The first group (PALM) relates to structural problems- it is thought that growths in or around the womb increase the surface area of the womb’s lining (increasing the amount of tissue/ blood loss) and/ or interfere with the normal constriction of muscle and blood vessels involved in stopping menstruation (i.e. prolonging the period) . These growths are categorised as; Polyps, Adenomyosis, Leiomyoma (aka fibroids!), and Malignancy (e.g. womb cancer). By far the most common of these causes are fibroids and polyps, then adenomyosis, and only very rarely, more serious issues such as womb cancer.
The second group (COEIN) relates to non-structural problems: Coagulopathy (i.e. blood clotting disorders- approx. 13% of HMB cases are caused by these e.g. Von Willebrand’s Disease ), Ovulatory Disorders (e.g. hormonal changes associated with the peri-menopause, Polycystic Ovary Syndrome, thyroid or pituitary gland disorders), Endometrium (e.g. a blood clotting issue found only in the lining of the womb- usually diagnosed after excluding all the other possibilities), Iatrogenic (non-biological chemical factors- e.g. cigarette smoking, the copper coil (IUD), hormonal contraception, anti-convulsant, antidepressant, or anti-psychotic medications, and antibiotics such as rifampin and griseofulvin) and, lastly, Not Yet Classified (other gynaecological issues may play a role in HMB but are difficult to identify- this category will develop as further research is conducted) .
Treatment options obviously vary according to the cause(s), but it is definitely worth taking iron supplements regardless, since iron-deficiency anaemia plays a large part in the life-affecting symptoms of HMB (i.e. fatigue) and can further increase menstrual blood loss .
A bonus note for clinicians/ menstrual health and rights enthusiasts;
A few years ago, it was decided to just trust that people who sought help from their doctor for very heavy periods, really did have them . This is actually a very nice intention; a decision to believe in female patients rather than dismiss them as ‘prone to exaggeration’ (which is sadly still a common experience). Unfortunately, menstruation education is typically of poor quality and so people who menstruate often do not have an informed idea if their flow is average, heavy- or even heavy enough to be Heavy Menstrual Bleeding (HMB).
It has been argued that it is better to treat all of those who think they have this condition, rather than measuring fluid/ blood loss or otherwise making a diagnostic distinction (e.g. asking the screening questions listed above) . However, I am concerned that by doing this we are actually reinforcing a sexist myth that positions all menstruating people as debilitated (the medicalisation of menstruation), as well as normalising the exceptionally severe experiences of those few who really do lose over 80 ml of blood per period (the minimisation of serious women’s health issues).
The impact – Clinical research on HMB has found that a significant proportion (sometimes the majority) of trial participants, actually have ‘normal’ menstrual flow, which obviously messes up the findings . Plus, the prevalence of Heavy Menstrual Bleeding can become highly exaggerated: A highly-cited UK study  simply asked people about their typical menstrual flow and roughly equated the subjective categories ‘variable’, ‘heavy’ and ‘very heavy’ with the sort of experiences described by people with HMB. Unsurprisingly, it reported an extremely high prevalence rate of debilitating blood loss in the UK population- around 25% ! This is not good for science or for society.
With menstrual cups, we now have a much simpler way to measure fluid loss/ estimate blood loss and so I think it is probably best to stick to the 160 ml fluid/80 ml blood loss categorisation, when deciding how best to treat an individual patient. For example, it may be that someone who has normal flow but feels it is ‘too heavy’ simply requires some further information about blood loss, how to manage periods, or perhaps even specific medical treatment for a different health issue (e.g. iron deficiency anaemia). They certainly should not be incorrectly categorised as having a serious health condition such as Heavy Menstrual Bleeding. Likewise, those who do have this condition, urgently require specific tests and specialist medical support, and should not be categorised as merely falling at the far end of the ‘normal’ curve when it comes to menstrual blood loss.
Cite as: King, S (2020) ‘Menstrual blood loss… What’s normal?’ Menstrual Matters Blog accessed [date] https://www.menstrual-matters.com/blog/bloodloss/