Women’s Health · Symptoms

Heavy Periods — What Causes Them and What a Scan Can Find

Heavy bleeding is common, treatable, and far too often written off as normal. Here is what actually counts as heavy, where it comes from, and what a pelvic ultrasound can and cannot tell you about it.

Period tracking calendar, hot water bottle and tea laid out on a blanket

Because periods are private, most people calibrate “normal” against their own history rather than anyone else’s — which is exactly how genuinely heavy bleeding gets tolerated for years. If your period dictates what you can wear, where you can go, or how you feel for a week each month, that is not a personality trait of your cycle. It is a symptom, and it usually has a findable cause.

The Threshold

What actually counts as heavy

Any of the following puts you in “worth assessing” territory: needing to change protection every hour or two; leaking through, or needing two forms of protection together; passing clots larger than a 10p coin; bleeding for more than seven days; getting up at night to change; or the tiredness and breathlessness of iron running low.

The formal definition — around 80 ml of blood loss a cycle — is not something anyone can measure at home, which is why the practical markers above are what clinicians actually use. One of them, consistently, is enough of a reason to look into it.

Causes

Where heavy bleeding comes from

Structural causes a scan can see. Fibroids are the most common — and the ones bulging into the womb cavity punch far above their size for bleeding. Endometrial polyps, and adenomyosis (lining tissue within the womb muscle), are the other frequent finds; our guide to monitoring fibroids covers what happens once one is found.

Causes a scan cannot see. Hormonal patterns — especially the irregular, heavier cycles of the years before menopause — thyroid problems, a copper coil, and clotting tendencies, which are worth suspecting when periods have been heavy since they first started. These need your GP and usually blood tests, not imaging.

And sometimes, nothing is found. Heavy bleeding with a completely normal scan and normal bloods is common. It has a name, it is real, and it is still very treatable — the scan’s job in that case was ruling the structural causes out.

Bleeding that changes the plan

Bleeding between periods or after sex that keeps happening should go to your GP. Any bleeding after menopause needs prompt assessment every time — our guide to postmenopausal bleeding explains why. And flooding with dizziness or faintness, or heavy bleeding with a possible pregnancy, needs same-day NHS care — call NHS 111 or go to A&E.

The Scan

What a pelvic ultrasound finds — and when to book it

A transvaginal scan gives the clearest view of the womb lining, which is where the answers to heavy bleeding usually sit. Timing matters more than most people expect: the lining reads best in the days just after a period finishes, when it is at its thinnest and a polyp or focal thickening stands out against it. Book mid-cycle and a normal thick lining can hide exactly what we are looking for.

The scan maps any fibroids — number, size and, critically, position relative to the cavity — looks for polyps and the muscle changes of adenomyosis, measures the lining, and checks both ovaries. What it cannot do is measure hormones, thyroid function or clotting; those are blood tests through your GP, and the two assessments work best together.

Hands holding a warm mug under a soft blanket while resting on a sofa
At IUS London

How the appointment runs

  1. 1
    BookingNo referral needed. Tell us where you are in your cycle and we will help you time the appointment for the days just after your period, when the lining reads best.
  2. 2
    The scanTransvaginal as standard for the clearest view of the lining, transabdominal available if you prefer. The appointment is 30 minutes.
  3. 3
    What we measureLining thickness and pattern, any polyp, a full fibroid map with positions relative to the cavity, adenomyosis features, and both ovaries.
  4. 4
    ResultsExplained on screen as we scan, with the written report usually with you within two hours — the structural half of the picture, ready for your GP to plan treatment around.
FAQs

Your questions answered

How much bleeding is officially too much?
The textbook figure is about 80 ml a cycle, which nobody can measure at home. In practice: protection changed every hour or two, flooding, clots bigger than a 10p coin, bleeding beyond seven days, or iron-deficiency tiredness. Any one of those, consistently, justifies assessment.
When in my cycle should I book the scan?
Just after your period finishes, when the lining is thinnest — polyps and focal thickening show most clearly against a thin lining. If your cycles are irregular, book anyway and tell us; we will read the lining against wherever you are.
Can small fibroids really cause heavy periods?
Yes — position beats size. A small fibroid bulging into the cavity can cause more bleeding than a much larger one in the outer wall. That is why the scan maps where each fibroid sits, not just how big it is.
Will the scan tell me what treatment I need?
It tells you what is structurally there, which is what treatment decisions rest on. The options themselves — from tranexamic acid and hormonal treatments to a coil or a procedure — are a conversation with your GP or gynaecologist, taken with the report in hand.
Could it just be perimenopause?
From the mid-forties, heavier and less predictable periods are common as ovulation becomes irregular. That makes assessment more worthwhile, not less — the same years are when fibroids and polyps are most common, and “probably perimenopause” should be a conclusion, not an assumption.
When is heavy bleeding urgent?
Flooding with dizziness or faintness, heavy bleeding when you might be pregnant, or any bleeding after menopause. The first two need same-day NHS care via 111 or A&E; the third needs a prompt GP appointment every time.
Related

Where to go from here

SymptomsPelvic Pain — When to Scan

What the pattern of pain suggests and when it needs same-day care.

Read the guide →FibroidsMonitoring Fibroids

When fibroids need watching and how surveillance works.

Read the guide →After MenopausePostmenopausal Bleeding

Why it always needs checking, and what the scan measures.

Read the guide →

See what is behind it

Lining, fibroid map, polyps, adenomyosis and both ovaries in one 30-minute appointment — timed to your cycle, explained on screen as we scan, with the written report usually with you within two hours.

From £159
Pelvic scan

Pelvic scan

5a Lucerne Mews
Kensington, London W8 4ED
3 mins from Notting Hill Gate

This article is general information about heavy menstrual bleeding, not individual medical advice. Persistent heavy bleeding deserves a GP assessment whatever a scan shows — NHS guidance on heavy periods covers the causes and the treatment options available.

Written and clinically reviewed by the HCPC-registered sonographers who perform this scan at IUS London — a CQC-registered diagnostic ultrasound clinic (Provider ID 1-2775844974). Your own findings are explained to you at the scan and set out in your report.

Author: Yianni Kiromitis, Senior Sonographer, HCPC RA38415 — over 20 years’ experience in NHS and private ultrasound
Medically reviewed: 9 August 2026