ObGyn Intelligence
ObGyn Intelligence ← All Tools — tools.obmd.com
How Heavy Is Heavy?

How Heavy Is Heavy?

A structured assessment of menstrual blood loss for patients and clinicians — built around the products people actually use.

The problem this tool exists to solve. There is no single definition of a heavy period, and the two definitions in circulation disagree with each other. The research definition is more than 80 mL of blood loss per cycle — that is about five and a half tablespoons, roughly a third of a measuring cup. The clinical definition, from NICE and adopted by FIGO and ACOG, is menstrual blood loss that interferes with a woman's physical, social, emotional and/or material quality of life. FIGO System 1 states plainly that flow volume is subjective and patient-determined.

The familiar bedside rule — "a pad an hour" — has been quantitatively invalidated. When 21 menstrual products were bench-tested with human red blood cells, capacity ranged from 1 mL for some period underwear to 80 mL for a menstrual disc. That is a roughly fifty-fold spread. The same sentence from two different patients can mean two entirely different volumes.

This tool therefore does three things separately and never collapses them into a single score: it estimates blood loss from the specific product used, it measures quality-of-life impact, and it checks the three clinical features shown to predict measured loss above 80 mL.

How to picture these amounts. Millilitres mean very little to most people, so this tool translates them.
• 1 teaspoon = 5 mL  •  1 tablespoon = 15 mL, about 3 teaspoons  •  1 measuring cup = about 240 mL
• The 80 mL research threshold = about 5½ tablespoons, or roughly a third of a measuring cup, spread over the whole period.
• The range FIGO calls normal is 5 to 80 mL — anywhere from about a teaspoon up to that third of a cup, across the entire period.
• The CDC puts a normal period at 2 to 3 tablespoons, and says women with heavy bleeding lose about twice that.
Three authorities, three answers. The CDC calls any period lasting more than 7 days heavy, and any product change sooner than every 2 hours heavy. FIGO calls 8 days or fewer a normal duration and leaves volume to the patient to judge. The measured-volume literature uses 80 mL and a change interval of under one hour. These are all current and they do not agree. This tool reports each one separately rather than pretending they reconcile. The CDC estimates heavy menstrual bleeding affects more than 10 million American women a year, roughly 1 in 5.
Scope. This tool assesses heavy menstrual bleeding only. It does not assess light or absent periods — no validated threshold for abnormally light flow exists, and FIGO does not operationalise one. It is not for bleeding in pregnancy, postmenopausal bleeding, or acute haemorrhage requiring immediate care.

Evidence base

Every number displayed by this tool traces to one of these publications.

  1. DeLoughery E, Colwill AC, Edelman A, Samuelson Bannow B. Red blood cell capacity of modern menstrual products: considerations for assessing heavy menstrual bleeding. BMJ Sex Reprod Health. 2024;50(1):21-6. doi:10.1136/bmjsrh-2023-201895. Primary source for every product capacity figure in this tool. Twenty-one commercially available products bench-tested with expired human packed red blood cells rather than saline. Supplies the entire estimation engine. PMID not confirmed at time of build; DOI verified.
  2. Munro MG, Critchley HOD, Fraser IS; FIGO Menstrual Disorders Committee. The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes of abnormal uterine bleeding in the reproductive years: 2018 revisions. Int J Gynaecol Obstet. 2018;143(3):393-408. doi:10.1002/ijgo.12666. PMID: 30198563. Source of the FIGO System 1 parameters (frequency, duration, regularity, volume, intermenstrual and unscheduled bleeding) and the PALM-COEIN framework used in the clinician output.
  3. Jain V, Munro MG, Critchley HOD. Contemporary evaluation of women and girls with abnormal uterine bleeding: FIGO Systems 1 and 2. Int J Gynecol Obstet. 2023;162(Suppl 2):29-42. doi:10.1002/ijgo.14946. PMID: 37538019. Confirms that flow volume in FIGO System 1 is patient-determined; supplies the age-dependent cycle regularity limits and the coagulopathy screening tool reported as approximately 90% sensitive.
  4. Warner PE, Critchley HOD, Lumsden MA, Campbell-Brown M, Douglas A, Murray GD. Menorrhagia I: measured blood loss, clinical features, and outcome in women with heavy periods: a survey with follow-up data. Am J Obstet Gynecol. 2004;190(5):1216-23. doi:10.1016/j.ajog.2003.11.015. PMID: 15167821. Source of the three-feature predictive model (low ferritin, clots larger than one inch, changing protection more often than hourly at full flow) and its performance: 76% correctly classified, sensitivity 60%, specificity 86%. Also the finding that only 34% (95% CI 28-40) of women referred for heavy periods exceeded 80 mL.
  5. National Institute for Health and Care Excellence. Heavy menstrual bleeding: assessment and management. NICE guideline NG88. London: NICE; 2018 (updated May 2021). Source of the quality-of-life definition of heavy menstrual bleeding adopted verbatim by FIGO and ACOG, and of the impact items used in the quality-of-life axis.
  6. Committee on Adolescent Health Care. Screening and management of bleeding disorders in adolescents with heavy menstrual bleeding. ACOG Committee Opinion No. 785. Obstet Gynecol. 2019;134(3):e71-83. doi:10.1097/AOG.0000000000003411. PMID: 31441820. Source of the adolescent pathway: routine serum ferritin, evaluation for bleeding disorder, iron deficiency identified at ferritin below 15 micrograms/L, iron loss of 0.4-0.5 mg per mL of blood, and the recommendation against routine imaging in this age group.
  7. Munro MG, Mast AE, Powers JM, Kouides PA, O'Brien SH, Richards T, et al. The relationship between heavy menstrual bleeding, iron deficiency, and iron deficiency anemia. Am J Obstet Gynecol. 2023;229(1):1-9. doi:10.1016/j.ajog.2023.01.017. PMID: 36706856. Supports iron status, rather than millilitres, as the clinically meaningful endpoint of heavy menstrual bleeding.
  8. Hallberg L, Högdahl AM, Nilsson L, Rybo G. Menstrual blood loss — a population study. Variation at different ages and attempts to define normality. Acta Obstet Gynecol Scand. 1966;45(3):320-51. doi:10.3109/00016346609158455. PMID: 5922481. Origin of the 80 mL threshold, chosen as the volume above which iron stores declined. Presented here as historical context, not as a bedside rule.
  9. Higham JM, O'Brien PM, Shaw RW. Assessment of menstrual blood loss using a pictorial chart. Br J Obstet Gynaecol. 1990;97(8):734-9. doi:10.1111/j.1471-0528.1990.tb16249.x. PMID: 2400752. The original Pictorial Blood Loss Assessment Chart, reported with sensitivity and specificity above 80% at a score of 100 in the derivation cohort. Deliberately not used as the scoring engine here — see the note below.
  10. Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities. About heavy menstrual bleeding. Atlanta (GA): CDC; 2024 May 15 [cited 2026 Jul 27]. Available from: https://www.cdc.gov/female-blood-disorders/about/heavy-menstrual-bleeding.html Source of the nine CDC signs reported as axis 4, the >7 day duration criterion, the 2-hour change criterion, the quarter-size clot threshold, the 2 to 3 tablespoon figure for a normal period, and the prevalence estimate of more than 10 million American women per year (about 1 in 5). Note that the page refers only to pads and tampons and does not address cups, discs or period underwear.
  11. Samuelson Bannow B, Rosovsky K, Chen K, Colwill A, Edelman A. Reusable menstrual hygiene products may lead to underdiagnosis of heavy menstrual bleeding: a randomised trial. BMJ Sex Reprod Health. 2025;51(4). doi:10.1136/bmjsrh-2024-202541. Supports the central premise that product type materially changes whether heavy menstrual bleeding is detected at all.
Where this tool departs from the CDC. The CDC page is high-sensitivity by design and is a good referral trigger, but three of its criteria do not survive contact with the measurement literature. Its 7-day duration rule treats duration as a proxy for volume, which FIGO 2018 explicitly separated. Its 2-hour change rule is twice as permissive as the only interval with published operating characteristics (Warner 2004: more often than hourly at full flow, specificity 86%). And it specifies pads and tampons without addressing cups, discs or period underwear, whose measured capacities span 1 to 80 mL. This tool reports the CDC criteria in full and unaltered, alongside the others, and shows where they diverge rather than silently resolving the conflict. Its clot threshold and its tablespoon anchor are, by contrast, consistent with the other sources: a US quarter is 24.3 mm, essentially Warner's one inch.
Why this tool does not use the PBAC. The Better You Know Menstrual Chart promoted on the CDC page is the Higham PBAC, scoring 1, 5 and 20 points for lightly stained, moderately soiled and fully saturated pads. It was derived and calibrated in 1990 on the pads and tampons of that era. It has no entries for menstrual cups, discs, or period underwear, and its scoring weights cannot be transferred to them. Rather than apply an instrument outside its validated domain, this tool uses measured product-specific capacities and asks directly how saturated each item was.
Stated limits of the estimation engine. The published capacities are saturation ceilings measured with packed red blood cells. Menstrual effluent is more viscous and contains secretions and endometrial tissue, so it behaves differently. The conversion from "about half full" to half the measured capacity is a linear approximation and has not been validated against alkaline haematin. Regular or medium pads were not separately reported and are bracketed between the published light and heavy figures. Treat every output as a range with real uncertainty, never as a measurement.
View:

About your periods

Answer what you can. Anything you are unsure about, leave on "not sure".

Get help now, before finishing this

Call your ObGyn, midwife, or emergency services now if you are soaking through a pad or tampon every hour for two hours in a row, if you feel faint, dizzy, breathless or your heart is racing, or if you are or might be pregnant and you are bleeding.

Age

Age changes what counts as a normal cycle and what should be checked.

Your period products

List up to three kinds of product you used across your whole last period. Count every item you used, all days added together. If you used four pads a day for five days, enter 20.

How your period affects your life

Tick anything that has happened in the last few months.

Clots, flooding and iron

These three questions carry more weight than the others.

Your cycle pattern

Bleeding and bruising

Bleeding disorders are a common and often missed cause of heavy periods.

How you have been feeling

Your results

Three separate findings. They are reported separately on purpose — they measure different things and often disagree.