Endometrial assessment is one of the highest-stakes measurements in gynaecological ultrasound. A single number — endometrial thickness in a postmenopausal woman with bleeding — routinely determines whether a patient proceeds to biopsy. That puts real weight on measuring it correctly.

How to Measure

Transvaginal is required. Transabdominal imaging cannot reliably measure the endometrium, and a transabdominal-only study in a patient with abnormal bleeding should say so rather than report a number.

Plane: True midsagittal view of the uterus, showing the endometrial stripe continuously from the fundus to the internal cervical os.

What to measure: The double-layer thickness — the full anteroposterior measurement of both endometrial layers at the thickest point, measured perpendicular to the endometrial stripe, excluding any intracavitary fluid.

If fluid is present in the cavity, measure each layer separately and report the sum of the two single layers. Including the fluid inflates the measurement and is a common error.

Technical Points That Change the Number

Get a true midline. An oblique plane cuts the endometrium tangentially and overestimates thickness.
Measure at the thickest point, not wherever the calipers happen to land.
A markedly retroverted or axial uterus, large fibroids, or adenomyosis can make the endometrium impossible to measure reliably. When that is the case, say the endometrium is not adequately visualized rather than reporting an unreliable number — this is a genuinely important reporting distinction, because "not visualized" prompts further evaluation while a falsely thin number is reassuring and wrong.

Thresholds

Postmenopausal With Bleeding

This is the critical scenario.

An endometrial thickness of 4 mm or less in a postmenopausal woman with bleeding carries a very low likelihood of endometrial carcinoma, and widely used consensus guidance treats this as sufficiently reassuring that biopsy is not automatically required.

Above 4 mm warrants tissue sampling or further evaluation.

Two important qualifications:

Recurrent or persistent bleeding warrants evaluation regardless of thickness. A thin endometrium does not exclude pathology in a woman who keeps bleeding, and some endometrial cancers — particularly type II histologies — can present with a thin stripe.
The threshold applies specifically to bleeding. It is not a screening threshold.

Postmenopausal Without Bleeding

More contentious, and there is no single agreed cutoff. Incidentally thickened endometrium in an asymptomatic postmenopausal woman is managed according to the degree of thickening, the presence of other features, and individual risk factors. Values in the region of 8–11 mm are variously cited as prompting consideration of further assessment. Report the measurement and any morphological abnormality; the management decision belongs with the clinician.

Premenopausal

There is no single normal value — thickness varies through the cycle, so the measurement is only interpretable alongside cycle day.

Phase	Typical double-layer thickness	Appearance
Menstrual	2–4 mm	Thin, irregular, may contain blood
Early proliferative	4–8 mm	Hypoechoic, developing three-layer pattern
Late proliferative / periovulatory	8–12 mm	Classic trilaminar pattern
Secretory	7–16 mm	Uniformly echogenic, thickest phase

Always document cycle day. A 14 mm endometrium is entirely normal in the secretory phase and abnormal on day 5.

Best timing for assessment in a premenopausal woman with abnormal bleeding is the early proliferative phase, days 4 to 6, when the endometrium is thinnest and focal lesions stand out most clearly.

Focal Lesions

Most abnormal bleeding with a thickened endometrium turns out to be focal, and distinguishing the two commonest lesions matters because they are managed differently.

Endometrial Polyp

Focal, echogenic lesion within the cavity
Preserves the endometrial–myometrial junction
Often surrounded by a thin rim of fluid, best seen in the early proliferative phase
Pedicle artery sign: a single feeding vessel entering the lesion on colour Doppler. This is the most useful discriminating feature — a solitary feeding vessel strongly favours a polyp.
May be single or multiple, sessile or pedunculated

Submucosal Fibroid

Hypoechoic rather than echogenic
Broad-based, arising from and continuous with the myometrium
Distorts or interrupts the endometrial–myometrial junction
Circumferential (rim) vascularity rather than a single pedicle
Often produces posterior acoustic shadowing or edge shadowing
May show calcification in degenerated lesions

Report the degree of intracavitary protrusion. Whether a submucosal fibroid is mostly within the cavity or mostly intramural determines whether it can be resected hysteroscopically, so the surgeon needs that detail rather than just "submucosal fibroid."

Concerning Features

Findings that raise concern for hyperplasia or malignancy:

Diffuse, markedly thickened, heterogeneous endometrium
Irregular or indistinct endometrial–myometrial junction — suggests possible myometrial invasion
Irregular, multivessel vascular pattern rather than a single pedicle
Intracavitary fluid alongside a thickened, irregular endometrium in a postmenopausal woman
Irregular endometrial surface

None of these is diagnostic. The report should describe them and recommend tissue sampling — the diagnosis is histological.

Saline Infusion Sonohysterography

SIS distends the cavity with sterile saline and is the single most useful next step when standard transvaginal imaging shows a thickened or irregular endometrium without a clear explanation.

What it adds: It separates the endometrial layers, so a focal lesion becomes obvious and can be characterized as a polyp versus a submucosal fibroid, and its size, location, and degree of intracavitary protrusion can be measured precisely.

Timing: Early proliferative phase, days 4 to 10, after bleeding has stopped and before the endometrium thickens.

Contraindications: Pregnancy, active pelvic infection. Exclude pregnancy before proceeding in any premenopausal patient.

Practical note: A negative SIS in a woman with a diffusely thickened endometrium does not remove the need for sampling — it tells you the thickening is diffuse rather than focal, which is itself clinically useful information.

Special Situations

Tamoxifen: Produces characteristic endometrial changes — thickening, subendometrial cysts, and a heterogeneous appearance — that make thickness measurement poorly predictive. Standard thresholds do not apply, and management is generally driven by symptoms rather than measurement. Note tamoxifen use prominently in the report.

Hormone replacement therapy: Sequential HRT produces cyclical changes; measure early in the cycle where possible and document the regimen.

Retained products of conception: Echogenic material in the cavity with vascularity on colour Doppler in a recently pregnant patient. Vascularity is the key feature distinguishing retained products from blood clot.

Key Images to Capture

Midsagittal uterus with endometrial thickness measurement
Transverse uterus at the level of maximum endometrial thickness
Endometrial–myometrial junction, documented as regular or irregular
Colour Doppler of any focal lesion, demonstrating the vascular pattern
Any intracavitary fluid, with single-layer measurements
Both ovaries
Cycle day or menopausal status documented

Reporting Language

Polyp: "Endometrial thickness 13 mm (day 6 of cycle). Within the cavity there is a 1.4 × 0.9 cm echogenic focal lesion with a single feeding vessel on colour Doppler. The endometrial–myometrial junction is preserved. Appearances favour an endometrial polyp. Saline infusion sonohysterography or hysteroscopy would confirm and allow assessment for resection."

Postmenopausal bleeding, reassuring: "Endometrial thickness 3 mm, uniform and regular, with a distinct endometrial–myometrial junction. No focal lesion or intracavitary fluid. In a postmenopausal woman with bleeding, an endometrial thickness of 4 mm or less carries a low likelihood of endometrial carcinoma. Persistent or recurrent bleeding warrants further evaluation regardless of this measurement."

SonoBuddy is a reference tool. Endometrial sampling decisions belong with the referring clinician.

Endometrial Assessment and Abnormal Uterine Bleeding