Normal Endometrial Thickness in Postmenopausal Women
In postmenopausal women, the endometrium should measure ≤4 mm by transvaginal ultrasound, which provides a negative predictive value for endometrial cancer of nearly 100%. 1
Threshold Values and Clinical Significance
The 4 mm cutoff is the established standard: An endometrial thickness ≤4 mm in postmenopausal women conveys a negative predictive value for endometrial cancer approaching 100% 2, 1
When endometrial thickness measures ≥5 mm, endometrial tissue sampling is generally recommended to exclude malignancy 1
The American College of Radiology specifically endorses this 4 mm threshold as the dividing line between normal and abnormal endometrial thickness in postmenopausal women 1
In the landmark Nordic multicenter study of 1,168 postmenopausal women with bleeding, no malignant endometrium measured less than 5 mm, and the mean thickness for atrophic endometrium was 3.9 ± 2.5 mm 3
Context-Dependent Thresholds
Asymptomatic Postmenopausal Women
For asymptomatic postmenopausal women without bleeding, a higher threshold of ≤11 mm is acceptable before considering biopsy 1, 4
At the 11 mm threshold in asymptomatic women, the risk of cancer is approximately 6.7% if thicker than 11 mm, but only 0.002% if ≤11 mm 4
This higher threshold for asymptomatic women is justified because the pretest probability of cancer is substantially lower without vaginal bleeding 4
Symptomatic Postmenopausal Women
For women with postmenopausal bleeding, maintain the strict 4 mm threshold for determining need for tissue sampling 1, 3
Even measurements of 5 mm warrant investigation in symptomatic women 1
Important Clinical Caveats
The European Society for Medical Oncology uses a slightly more conservative cutoff of ≤3 mm, though this is less widely adopted than the 4 mm standard 1
If repeat imaging continues to show endometrium <4 mm in a postmenopausal woman, the negative predictive value for cancer remains nearly 100%, even if initial evaluation was negative 2, 1
Transvaginal ultrasound is sensitive for measuring endometrial thickness but cannot reliably determine the etiology of endometrial thickening - tissue diagnosis is required for thickened endometrium 1
In research studies, 89% of type I endometrial cancers and 93% of type II endometrial cancers had endometrial thickness >4 mm, confirming the reliability of this threshold across histologic subtypes 5
Measurement Technique
Transvaginal ultrasound should be combined with transabdominal ultrasound whenever possible for complete pelvic assessment 1
The measurement should include both endometrial layers using the double-layer technique 3
Doppler evaluation of endometrial vascularity can help identify vessels within polyps or cancer, though it cannot definitively differentiate benign from malignant lesions 2