Abnormal uterine bleeding and endometrial assessment

ACR AC Abnormal Uterine Bleeding

Transvaginal ultrasound is the initial test for abnormal uterine bleeding at any age. In postmenopausal bleeding it functions as a triage test for endometrial sampling; in premenopausal bleeding it is a structural assessment, and endometrial thickness is not interpretable in the same way.

Postmenopausal bleeding, or heavy, intermenstrual or unscheduled bleeding in a premenopausal woman or one on hormonal treatment.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Pelvic ultrasound — transabdominal and transvaginal

Ultrasound pelvis (transabdominal ± transvaginal)

What we'd amend, and why

Transvaginal ultrasound measures the endometrium reliably and simultaneously explains most structural causes of bleeding — submucosal fibroids, polyps, adenomyosis. In postmenopausal bleeding it functions as a triage test: a thin, uniform, well-visualised endometrium at or below the local threshold — commonly 4 mm, quoted between 3 and 5 mm by different bodies — has a high negative predictive value for carcinoma and is what allows a large proportion of women to avoid an invasive procedure, while a thicker, heterogeneous, focally abnormal or unmeasurable endometrium sends them on to sampling. The threshold is a triage tool, not a discharge: recurrent or persistent bleeding needs tissue whatever the measurement, the measurement is uninterpretable on tamoxifen, and the recent re-evaluation of the cut-off found it less sensitive in Black women, where the threshold for sampling should be lower.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayany — All patients

Decision support only. Local protocol takes precedence.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Is the patient postmenopausal, and is she on tamoxifen, HRT or another hormonal treatment?
It determines how endometrial thickness should be interpreted and whether an apparently thickened endometrium is expected.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

All patients

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Ultrasound pelvis (transabdominal ± transvaginal) Pelvic ultrasound — transabdominal and transvaginal usually appropriate	Transvaginal ultrasound measures the endometrium reliably and simultaneously explains most structural causes of bleeding — submucosal fibroids, polyps, adenomyosis. In postmenopausal bleeding it functions as a triage test: a thin, uniform, well-visualised endometrium at or below the local threshold — commonly 4 mm, quoted between 3 and 5 mm by different bodies — has a high negative predictive value for carcinoma and is what allows a large proportion of women to avoid an invasive procedure, while a thicker, heterogeneous, focally abnormal or unmeasurable endometrium sends them on to sampling. The threshold is a triage tool, not a discharge: recurrent or persistent bleeding needs tissue whatever the measurement, the measurement is uninterpretable on tamoxifen, and the recent re-evaluation of the cut-off found it less sensitive in Black women, where the threshold for sampling should be lower.
Problem solving	MRI Pelvis (Gynaecological) MRI Pelvis — endometrial cancer staging	Once endometrial carcinoma is proven histologically, MRI defines depth of myometrial invasion, cervical stromal involvement and nodal disease, which is what determines the extent of surgery and whether the patient needs a specialist centre. It is a staging study, not a diagnostic one.

Where the endometrium cannot be adequately measured — axial uterus, fibroids, previous surgery — the correct next step is usually hysteroscopy and sampling rather than another imaging test.

Pitfalls

Applying postmenopausal thickness thresholds to a premenopausal woman, where the endometrium varies through the cycle and a measurement alone means little.
Reporting a thin endometrium as reassuring in a woman with recurrent postmenopausal bleeding — persistent bleeding needs tissue regardless of the measurement.
Missing a focal lesion within a thin endometrium; a polyp or focal cancer can sit inside an otherwise normal-thickness stripe.
Requesting MRI to work out whether a bleeding endometrium is malignant. That is a histological question.
Overlooking the tamoxifen effect and calling the subendometrial cystic change cancer, or dismissing genuine pathology as drug effect.
Applying the thin-endometrium threshold to a woman on tamoxifen. The measurement carries no negative predictive value in that group, and a thickness-based reassurance is how a tamoxifen-associated carcinoma is missed.
Reporting a measurement without saying whether the endometrium was adequately visualised. "4 mm" from a stripe obscured by fibroids or an axial uterus is not a reassuring 4 mm — it is a non-diagnostic study, and it should be reported as one so the patient goes to hysteroscopy rather than home.

Priors — what to pull first

Retrieve any previous endometrial sampling or hysteroscopy; a recent benign biopsy changes what a thickened endometrium means today.
Prior ultrasounds establish whether a fibroid or polyp is new or long-standing.

What makes a good request

Say whether the woman is postmenopausal and what hormonal treatment she is on, including tamoxifen: the thresholds and the appearances differ.
The number that matters is the endometrial thickness in postmenopausal bleeding. A uniform, well-visualised endometrium of 4 mm or less carries a very high negative predictive value for carcinoma and, in a woman not on hormonal treatment, allows sampling to be avoided at first presentation; above 4 mm, or where the stripe is heterogeneous, focal or cannot be measured, the pathway is tissue. Thresholds are quoted between 3 and 5 mm by different bodies and this is a threshold to confirm locally, not a rule to import.
That threshold is a triage tool with known limits. The 2024 systematic review re-evaluating it found materially lower sensitivity in Black women, in whom non-endometrioid cancers and coexisting fibroids are commoner, so a thin stripe should carry less weight and the threshold for proceeding to sampling should be lower — a measurement is not a substitute for the clinical decision.
Endometrial thickness is not interpretable at all on tamoxifen. The drug produces subendometrial cystic change and a spuriously thick, heterogeneous stripe, so a woman bleeding on tamoxifen goes to hysteroscopy and sampling whatever the measurement says.
MRI has no role in the initial assessment of bleeding. It stages a cancer that has already been diagnosed histologically.

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Pelvic ultrasound — transabdominal and transvaginal MRI Pelvis — endometrial cancer staging

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.