The basics
Why nobody agrees on what "heavy" means
1 min read
Three definitions are in current use, and they identify different women. None is wrong; each was built for a different purpose.
| Definition | Threshold | Built for |
|---|---|---|
| Research / volumetric | More than 80 mL of measured blood loss per cycle | Trials and physiology. Not measurable in ordinary life. |
| NICE, adopted by FIGO and ACOG | Blood loss that interferes with physical, emotional, social or material quality of life | Clinical care. Puts the patient's experience at the centre. |
| CDC | Bleeding lasting more than 7 days, or soaking through a pad or tampon more often than every 2 hours | Public health screening. Fast, countable, no judgment call. |
A woman can meet the CDC criteria and fall under 80 mL. She can lose well over 80 mL and say her life is unaffected. Both are common, and neither is an error. Rather than reconciling the three, the How Heavy Is Heavy? tool reports each separately and tells you when they disagree — because the disagreement is itself clinically useful.
The measurement problem nobody mentions
Estimating volume from products only works if the product reached the end of its useful life at the moment it was changed. Changed on a schedule and not full, the estimate runs high. Already at capacity or leaking before the change, the estimate runs low — and the interval it took to fill reveals the peak flow rate, which often matters more than the daily total. The tool asks about this directly instead of assuming.
The second complication is modern products. Cups, discs and period underwear hold far more than pads and tampons, and marketed capacity is not interchangeable with red-blood-cell volume. Published capacity measurements, not label claims, are what the tool uses.