Normal Endometrial Thickness in Postmenopausal Women
In postmenopausal women, the normal endometrial lining should measure ≤4 mm on transvaginal ultrasound, which provides a negative predictive value for endometrial cancer of nearly 100%. 1
Threshold for Normal Endometrial Thickness
The American College of Radiology establishes ≤4 mm as the upper limit of normal endometrial thickness in postmenopausal women, with this measurement providing excellent reassurance against malignancy. 1
When the endometrium measures ≥5 mm in a postmenopausal woman, endometrial tissue sampling is generally recommended due to increased cancer risk. 1
The European Society for Medical Oncology uses a slightly more conservative threshold of ≤3 mm, though the 4 mm cutoff is more widely accepted in clinical practice. 1
Evidence Supporting the 4 mm Threshold
In asymptomatic postmenopausal women not on hormone replacement therapy, 77.1% have an endometrial thickness ≤4 mm and 92% measure ≤5 mm, with a mean thickness of 3.71 ± 1.9 mm. 2
For asymptomatic postmenopausal women, an 11 mm threshold separates high-risk (6.7% cancer risk) from low-risk (0.002% cancer risk) populations, but this applies specifically to the decision for biopsy rather than defining "normal." 3
Research demonstrates that postmenopausal women without bleeding have an average endometrial thickness of 1.4 ± 0.7 mm (range 1-5 mm). 4
Clinical Management Algorithm
For Endometrial Thickness ≤4 mm:
- No further evaluation is needed if the patient is asymptomatic, as the negative predictive value for cancer remains nearly 100%. 1
- If repeat imaging is performed and the endometrium remains <4 mm, the negative predictive value for cancer continues to be nearly 100%. 1
For Endometrial Thickness ≥5 mm:
- Endometrial tissue sampling is mandatory using Pipelle or Vabra devices, which demonstrate sensitivities of 99.6% and 97.1% respectively for detecting endometrial carcinoma. 1
- Transvaginal ultrasound combined with transabdominal ultrasound should be performed for complete pelvic assessment. 1
For Endometrial Thickness >11 mm (Asymptomatic Women):
- Tissue sampling is required as this represents a significant risk factor for endometrial hyperplasia or malignancy, with cancer risk of 6.7%. 5, 3
Important Clinical Caveats
Transvaginal ultrasound is sensitive for measuring endometrial thickness but cannot reliably determine the etiology of endometrial thickening—tissue diagnosis is required for definitive assessment. 1
Abnormal echogenicity and texture of the endometrium correlate with significant pathology even when thickness appears normal. 1
Echogenic fluid within the endometrial cavity is a critical red flag: it carries an odds ratio of 10.94 for malignancy and mandates endometrial sampling regardless of endometrial thickness. 6
If endometrial thickness is ≤3 mm with clear fluid, endometrial sampling may not be necessary, but endocervical sampling should be considered to exclude endocervical cancer. 6
Sonohysterography can distinguish between focal and diffuse pathology when initial transvaginal ultrasound demonstrates focal abnormalities. 1
Age-Related Considerations
- Cancer risk increases with age at every endometrial thickness measurement: using the 11 mm threshold, cancer risk increases from 4.1% at age 50 to 9.3% at age 79. 3