Normal Endometrial Thickness
In postmenopausal women, normal endometrial thickness is ≤4 mm, while in premenopausal women, endometrial thickness varies with the menstrual cycle and has no validated upper limit cutoff. 1
Postmenopausal Women
The critical threshold for postmenopausal women is 4 mm or less, which conveys a negative predictive value for endometrial cancer of nearly 100%. 1, 2
Key Thresholds and Actions:
- ≤4 mm: Considered normal; no further evaluation needed if asymptomatic 1, 2
- ≥5 mm: Prompts endometrial tissue sampling due to increased cancer risk 1, 2
Clinical Context:
- The mean endometrial thickness in asymptomatic postmenopausal women is approximately 2.9 mm (95% CI, 2.6-3.3 mm) 3
- Endometrial thickness correlates with body weight and body mass index in postmenopausal women 4
- For asymptomatic postmenopausal women without bleeding, an 11 mm threshold has been proposed, as thickness >11 mm carries approximately 6.7% cancer risk 5
Important Caveats:
- Transvaginal ultrasound (TVUS) is sensitive for measuring endometrial thickness but cannot reliably determine the etiology of thickening 1
- Abnormal echogenicity and texture of the endometrium correlate with significant pathology even when thickness appears normal 1
- The European Society for Medical Oncology uses a slightly more conservative cut-off of ≤3 mm 2
Premenopausal Women
In premenopausal women, endometrial thickness varies throughout the menstrual cycle, and there is no validated absolute upper limit cutoff. 1
Critical Clinical Points:
- Endometrial thickness is NOT a reliable indicator of endometrial pathology in premenopausal women 1
- Even with thickness <5 mm, endometrial polyps or other pathology may be present 1
- The thickness changes physiologically with hormonal fluctuations during the menstrual cycle 1
Diagnostic Approach:
- Focus on abnormal echogenicity and texture rather than absolute thickness measurements 1
- Clinical symptoms (abnormal uterine bleeding) should drive further evaluation, not thickness alone 1
Common Pitfalls to Avoid:
- Do not apply postmenopausal thresholds to premenopausal women - the physiology is fundamentally different 1
- Do not rely solely on endometrial thickness measurement - always consider echogenicity, texture, and clinical presentation 1
- Do not use endometrial thickness as a screening tool in asymptomatic postmenopausal women - the prevalence of malignancy is too low (0.62%) to justify routine screening 3
- In women taking selective progesterone receptor modulators (like ulipristal acetate), endometrial thickness may increase to >16 mm in 11% of patients without pathological significance 1