Transvaginal Ultrasound and Endometrial Thickness
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Direct answer
Endometrial thickness on transvaginal ultrasound is the double-layer measurement of the endometrium in its longest sagittal section, and it varies widely with menstrual phase and menopausal status. In a postmenopausal woman without bleeding, a thickness of about 4 mm or less is generally reassuring. Postmenopausal bleeding with a thicker endometrium usually prompts biopsy, so the number always needs clinical context.
What you must remember
- Measurement: the double-layer thickness is taken in the longest sagittal plane, adding the anterior and posterior layers at the thickest point.
- Postmenopause: without bleeding, a thickness up to about 4 mm is usually reassuring, although some guidelines accept up to 5 mm; with bleeding, a thickness above the threshold prompts endometrial sampling.
- Premenopause: thickness is thin during menstruation, grows through the proliferative phase and is greatest in the secretory phase.
- Triple-line pattern: a three-layer appearance is typical of the proliferative phase, whereas a homogeneous hyperechoic endometrium suggests the secretory phase.
- Hyperplasia and carcinoma: a thickened, heterogeneous endometrium with irregular margins raises concern and needs tissue diagnosis.
- Polyps and fibroids: a focal lesion with a vascular stalk suggests a polyp, while a bulging hypoechoic mass suggests a submucous fibroid.
- Saline infusion sonography: distending the cavity with saline sharpens focal lesions and separates polyps from diffuse thickening.
Linking sonographic patterns to causes
Consider a 58-year-old woman with postmenopausal bleeding whose endometrium measures 6 mm. Her result must be read against her menopausal status, bleeding history and the appearance of the layer, since no single feature decides the diagnosis. The table links common appearances to their usual causes and the next step.
| Appearance | Usual cause | Next step |
|---|---|---|
| Thin and uniform, 4 mm or less | Atrophy after menopause | Usually none if there is no bleeding |
| Triple-line pattern | Proliferative phase | Interpret with cycle timing |
| Homogeneous hyperechoic thick layer | Secretory phase | Normal in the luteal phase |
| Thick and heterogeneous | Hyperplasia or carcinoma | Endometrial biopsy |
| Focal echogenic lesion with a vessel | Endometrial polyp | Hysteroscopy or biopsy |
| Hypoechoic mass bulging into cavity | Submucous fibroid | Hysteroscopic assessment |
The measurement alone does not decide management, because the pattern and the bleeding status change what a given thickness means. In postmenopausal bleeding, a thickened or heterogeneous endometrium is the trigger for tissue sampling, not the number on its own. Hormone therapy and tamoxifen change the expected thickness, so their use must be recorded alongside every measurement.
Where the exam tries to catch you
Questions here test whether the student reads the thickness against menopausal status, cycle phase and bleeding.
- Trap: Reassuring a postmenopausal woman with bleeding because the endometrium is only 5 mm. Correct: Postmenopausal bleeding with a thickness above the 4 mm threshold needs endometrial sampling, because ultrasound cannot exclude cancer alone.
- Trap: Calling a 12 mm endometrium abnormal in a premenopausal woman. Correct: Thickness rises through the cycle, so a value in the luteal phase may be normal, and cycle timing is essential.
- Trap: Using Doppler flow alone to exclude malignancy. Correct: Vascularity varies widely and cannot replace histology, which remains the standard.
- Trap: Measuring the endometrium as a single layer. Correct: The double-layer measurement is the standard, so a single-layer reading understates the true thickness.
Frequently asked questions
What is the normal endometrial thickness in postmenopausal women?
In postmenopausal women not on hormone therapy, an endometrial thickness of about 4 mm or less is generally reassuring when there is no bleeding. Some guidelines accept up to 5 mm. Bleeding changes the meaning of the reading, and a thicker endometrium then warrants biopsy.
At what endometrial thickness is biopsy indicated after postmenopausal bleeding?
Endometrial sampling is generally indicated for postmenopausal bleeding when the endometrium measures above about 4 mm. Ultrasound thickness alone does not exclude carcinoma, so tissue diagnosis is needed. A focal lesion or heterogeneous pattern lowers the threshold for sampling further.
How does endometrial thickness change through the menstrual cycle?
Endometrial thickness is thinnest during menstruation and grows through the proliferative phase, reaching its greatest in the secretory phase after ovulation. Mid-luteal values can reach the mid-teens in millimetres. Measurements must therefore always be interpreted against the day of the cycle.
What does saline infusion sonography add to endometrial assessment?
Saline infusion sonography distends the uterine cavity with saline, which outlines the endometrium and separates focal lesions such as polyps from diffuse thickening. It improves detection of intracavitary lesions compared with routine transvaginal scanning. It is a useful adjunct but does not replace histology.