Concerning Endometrial Thickness
In postmenopausal women, an endometrial thickness ≥5 mm is concerning and warrants tissue sampling, while in premenopausal women there is no validated absolute upper limit cutoff, and thickness alone is not a reliable indicator of pathology. 1
Postmenopausal Women
Threshold for Concern and Action
An endometrial thickness of 4 mm or less conveys a negative predictive value for endometrial cancer of nearly 100% in postmenopausal women, making it the reassuring threshold. 1, 2
When endometrial thickness measures ≥5 mm, endometrial tissue sampling is generally recommended to exclude malignancy, hyperplasia, or polyps. 1, 2
The European Society for Medical Oncology uses a slightly more conservative cutoff of ≤3 mm, though the 4 mm threshold is more widely adopted in North American guidelines. 2
Risk Stratification by Thickness
For asymptomatic postmenopausal women with endometrial thickness ≥10 mm, the malignancy risk rises to 11.4-16.3%, making investigation mandatory at this threshold. 2, 3
The optimal critical value for predicting malignancy in one study was 9.5 mm, with sensitivity and specificity of approximately 71-72%. 4
Using a threshold of ≥10 mm to prompt investigation has 100% sensitivity for detecting atypical hyperplasia and cancer, meaning no cases are missed at this cutoff. 3
Diagnostic Approach
Transvaginal ultrasound combined with transabdominal ultrasound is the first-line screening test for evaluating endometrial thickness in postmenopausal women. 1, 2
Endometrial sampling using Pipelle or Vabra devices achieves sensitivities of 99.6% and 97.1% respectively for detecting endometrial carcinoma when adequate tissue is obtained. 2, 5
If office endometrial biopsy is negative or inadequate in a symptomatic woman, escalation to hysteroscopy with directed biopsy or fractional D&C is mandatory, as blind sampling has a 10% false-negative rate. 2, 6
Critical Caveats for Postmenopausal Women
Ultrasound is sensitive for measuring thickness but cannot reliably determine the etiology of endometrial thickening—it cannot distinguish between polyps, hyperplasia, and malignancy. 1, 5
Abnormal echogenicity and texture of the endometrium correlate with significant pathology even when thickness is normal, so visual characteristics matter beyond millimeters. 1, 5
In asymptomatic postmenopausal women, the most common finding with thickened endometrium is endometrial polyps (74.3%), but 3.9% harbor malignancy. 7
Premenopausal Women
Lack of Validated Threshold
There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women, as thickness varies physiologically with menstrual cycle phase. 1
Endometrial thickness in premenopausal women is not a reliable indicator of endometrial pathology—even thickness <5 mm does not exclude polyps or other lesions. 1
Normal endometrial thickness varies with menstrual cycle: thinnest during early proliferative phase (days 4-6) and thickest during secretory phase. 1
When to Investigate Despite Normal Variation
Women ≥45 years with abnormal uterine bleeding should undergo endometrial sampling regardless of ultrasound findings, due to increased risk of hyperplasia and carcinoma from anovulatory cycles. 6
Premenopausal women with risk factors (unopposed estrogen exposure, PCOS, tamoxifen, obesity, nulliparity) warrant endometrial biopsy even without a specific thickness threshold. 6
Diagnostic Strategy
Transvaginal ultrasound should assess endometrial thickness, texture, echogenicity, and presence of focal lesions rather than relying on thickness measurement alone. 1, 6
Saline infusion sonohysterography demonstrates 96-100% sensitivity for detecting endometrial pathology and should be used when focal lesions are suspected or standard ultrasound is inadequate. 2, 6
Common Pitfalls to Avoid
Never accept a negative office endometrial biopsy as definitive in a symptomatic postmenopausal woman—the 10% false-negative rate mandates hysteroscopy if symptoms persist. 2, 6
Do not assume stable imaging excludes malignancy—tissue diagnosis is mandatory before any surgical intervention in postmenopausal bleeding. 2
Do not rely solely on thickness measurement without considering echogenicity, texture, and focal lesions, as these visual characteristics improve diagnostic accuracy. 1, 5
In premenopausal women, do not use thickness cutoffs to exclude pathology—symptomatic women and those with risk factors require tissue sampling regardless of measurements. 1, 6