Normal Endometrial Stripe Thickness
The normal endometrial thickness varies by menopausal status, with postmenopausal women having a normal thickness of 4 mm or less, while premenopausal women have normal measurements that vary throughout the menstrual cycle, ranging from approximately 3-13 mm. 1, 2
Normal Endometrial Thickness by Menopausal Status
Postmenopausal Women
- In postmenopausal women, the endometrial lining should measure 4 mm or less in thickness on transvaginal ultrasound 2
- An endometrial thickness of 4 mm or less in postmenopausal women has a negative predictive value for endometrial cancer approaching 100% 2
- When the endometrium measures ≥5 mm in a postmenopausal woman, endometrial tissue sampling is generally recommended 2
- The average thickness of endometrium for postmenopausal women without bleeding is approximately 1.4 ± 0.7 mm (range 1-5 mm) 3
- Endometrial thickness in postmenopausal women varies with years since menopause, with a mean of 2.3 mm during the first 5 years after menopause, decreasing to a stable mean of 1.8 mm between 5-13 years post-menopause 4
Premenopausal Women
- In premenopausal women with normal ovulatory cycles, endometrial thickness varies throughout the menstrual cycle 1, 3:
- There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women 1
- Using an endometrial stripe cutoff of 5 mm in premenopausal women would miss significant intracavitary pathology 5
Clinical Significance and Evaluation
Postmenopausal Women
- Endometrial thickness ≥5 mm in postmenopausal women has been associated with endometrial hyperplasia, polyps, or malignancy 1
- Transvaginal ultrasound should be the first-line screening test for endometrial assessment 2
- When endometrial thickness exceeds 4 mm in postmenopausal women, further evaluation with endometrial sampling is warranted 2
- Abnormal echogenicity and texture of the endometrium correlate with underlying uterine pathology regardless of thickness 1, 2
Premenopausal Women
- The sonographic evaluation of abnormal uterine bleeding in premenopausal women should include sonohysterography regardless of endometrial stripe thickness 5
- In a study of premenopausal women with an endometrial stripe measurement less than 5 mm, 11 had endometrial polyps and 5 had submucosal fibroids on sonohysterography, indicating that thin endometrium does not exclude pathology 5
Diagnostic Approach
- Transvaginal ultrasound should be combined with transabdominal ultrasound for complete assessment of pelvic structures 1, 2
- Color and spectral Doppler should be used to evaluate internal vascularity 1
- Sonohysterography may be considered to further characterize endometrial abnormalities when initial ultrasound findings are inconclusive 1, 2
- Endometrial sampling techniques like Pipelle or Vabra devices are highly sensitive for detecting endometrial carcinoma 2
Pitfalls and Caveats
- While endometrial thickness measurement is sensitive, it cannot reliably determine the etiology of endometrial thickening 1, 2
- The presence of endometrial fluid detected by transvaginal ultrasonography may be a marker for pathological changes of the endometrium in postmenopausal women if the endometrial thickness is greater than 4 mm 6
- Some guidelines, such as those from the European Society for Medical Oncology, recommend a more conservative cut-off of ≤3 mm for postmenopausal women 2