Maximum Normal Endometrial Thickness
In postmenopausal women, the maximum normal endometrial thickness is ≤4 mm, while in premenopausal women there is no validated absolute upper limit as thickness varies physiologically throughout the menstrual cycle. 1
Postmenopausal Women
The critical threshold of ≤4 mm conveys a negative predictive value for endometrial cancer of nearly 100%. 1, 2
Key Thresholds:
- ≤4 mm: Normal; no further evaluation needed if asymptomatic 1, 2
- ≥5 mm: Prompts endometrial tissue sampling due to increased cancer risk 1, 2
- The European Society for Medical Oncology uses a slightly more conservative cut-off of ≤3 mm 1, 2
Supporting Evidence:
- In asymptomatic postmenopausal women not using hormone replacement therapy, the estimated mean endometrial thickness is 2.9 mm (95% CI, 2.6-3.3 mm) 3
- Research in women without abnormal uterine bleeding found that endometrial cancer manifested with a mean thickness of 11.2 mm, being on average 2.4 mm thicker than benign counterparts 4
- If repeat imaging shows the endometrium remains <4 mm, the negative predictive value for cancer remains nearly 100% 2
Important Caveats:
- Transvaginal ultrasound is sensitive for measuring endometrial thickness but cannot reliably determine the etiology of thickening 1, 2
- Abnormal echogenicity and texture correlate with significant underlying pathology even when thickness is normal 2
- Consider echogenicity, texture, and clinical presentation rather than relying solely on thickness measurement 1
Premenopausal Women
There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women. 1
Physiologic Variation:
- Endometrial thickness varies throughout the menstrual cycle with hormonal fluctuations 1
- 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
Clinical 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
- Do not apply postmenopausal thresholds to premenopausal women, as the physiology is fundamentally different 1
Typical Cycle Measurements:
- Research in women on continuous-sequential hormone replacement therapy showed mean endometrial thickness of 4.3 mm at day 7 (immediately after withdrawal bleeding), increasing to 6.6-7.8 mm later in the cycle 5
- In BRCA mutation carriers (as a reference for normal variation), median follicular endometrial thickness was 7.0 mm (range 3-13 mm) and median luteal thickness was 10.85 mm (range 5-18 mm) 6
Special Populations
Women on Hormone Replacement Therapy:
- The optimal timing for monitoring endometrial thickness during continuous-sequential HRT is immediately after withdrawal bleeding, when mean thickness is lowest (approximately 4.3 mm) 5
- After six cycles of HRT, mean endometrial thickness increases from baseline (2.8 mm to 4.2 mm) 5
Women on Selective Progesterone Receptor Modulators:
- Endometrial thickness may increase without pathological significance 1