Normal Endometrial Thickness
Normal endometrial thickness varies dramatically based on menopausal status: in reproductive-age women it ranges from 2-4 mm during menstruation to 8-14 mm in the late luteal phase with no validated upper limit, while in postmenopausal women it should be ≤4 mm. 1
Reproductive-Age Women
Menstrual Cycle Variation
- Endometrial thickness fluctuates throughout the menstrual cycle and must always be correlated with cycle day for accurate interpretation. 1
- During menstruation: approximately 2-4 mm 1
- Proliferative phase: progressively thickens
- Late secretory/luteal phase: 8-14 mm 1
- A measurement of 6.6 mm may be entirely normal depending on menstrual cycle phase 1, 2
Key Clinical Points
- There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women. 1, 2
- Timing of ultrasound assessment is critical—always correlate with the patient's menstrual cycle day 1
- Abnormal echogenicity and texture correlate with underlying pathology regardless of thickness 1, 2
Postmenopausal Women
Normal Thickness and Thresholds
- The endometrial lining should be ≤4 mm in postmenopausal women, which conveys a negative predictive value for endometrial cancer approaching 100%. 1, 3
- When endometrial thickness is ≥5 mm, endometrial tissue sampling is generally recommended 1, 2, 3
- The mean endometrial thickness in asymptomatic postmenopausal women is approximately 2.9 mm (95% CI, 2.6-3.3 mm) 4
Clinical Context
- Endometrial thickness correlates with body weight and body mass index in postmenopausal women 5
- In women with endometrial cancer, mean thickness is 18.2 ± 6.2 mm compared to 3.4 ± 1.2 mm in those with atrophic endometrium 6
- The prevalence of endometrial carcinoma in asymptomatic postmenopausal women is 0.62% (95% CI, 0.42-0.82%) 4
Diagnostic Approach
Imaging Technique
- Transvaginal ultrasound should be combined with transabdominal ultrasound for complete pelvic assessment 2, 3
- Color and spectral Doppler should be used to evaluate internal vascularity 2
- Ultrasound is sensitive for measuring thickness but cannot reliably determine the etiology of endometrial thickening 1, 2, 3
When to Sample
- For postmenopausal women with endometrial thickness ≥5 mm, endometrial tissue sampling is mandatory. 2, 3
- Pipelle or Vabra devices have sensitivities of 99.6% and 97.1% respectively for detecting endometrial carcinoma 3
- Hysteroscopy with directed biopsy is preferred over blind sampling for focal lesions 3
Common Pitfalls
- Do not use a single thickness cutoff for premenopausal women—always consider menstrual cycle phase. 1
- Do not assume normal thickness excludes pathology if echogenicity or texture is abnormal 1, 2
- In postmenopausal women on hormone replacement therapy, measure thickness immediately after withdrawal bleeding for most reliable assessment 7
- Some guidelines recommend a more conservative ≤3 mm cutoff for postmenopausal women 3