What is the normal endometrial thickness for a postmenopausal woman?

Normal Endometrial Thickness in Postmenopausal Women

In postmenopausal women, an endometrial thickness of ≤4 mm is considered normal and conveys a negative predictive value for endometrial cancer of nearly 100%. 1

Diagnostic Thresholds and Clinical Significance

The American College of Radiology recommends the following thresholds for endometrial thickness in postmenopausal women:

• ≤4 mm: Normal, with nearly 100% negative predictive value for endometrial cancer 1
• ≥5 mm: Generally prompts evaluation by endometrial tissue sampling, particularly in the presence of vaginal bleeding 1
• ≥11 mm: Warrants investigation even in asymptomatic postmenopausal women 1

Research evidence supports these thresholds:

• A 1991 study suggested 5 mm as an appropriate cut-off level for conservative management of patients with postmenopausal bleeding 2
• More recent research (2018) found that using a threshold of ≥10 mm for investigation in asymptomatic women had 100% sensitivity for detecting endometrial atypical hyperplasia and cancer 3

Management Recommendations Based on Endometrial Thickness

Asymptomatic Postmenopausal Women:

• <4 mm: No further evaluation needed
• 4-10 mm: Consider case-by-case evaluation based on risk factors 4
• ≥10 mm: Endometrial biopsy or outpatient hysteroscopy recommended 4, 3

Postmenopausal Women with Bleeding:

• Any endometrial thickness: Should be evaluated, regardless of measurement 1
• ≤4 mm: Very low risk of malignancy, but clinical evaluation still warranted 1, 2
• >4 mm: Endometrial sampling indicated 1

Risk Factors That Influence Interpretation

Several factors may affect endometrial thickness measurements and cancer risk:

• Hormone replacement therapy: Women on unopposed estrogen or continuous estrogen and progestogen with endometrial thickness between 0.8-1.5 cm should undergo biopsy 5
• Body weight: Endometrial thickness correlates with body weight and BMI in postmenopausal women 6
• Other risk factors: Obesity (BMI >30), diabetes mellitus, hypertension, and Lynch syndrome increase endometrial cancer risk 1

Common Pitfalls to Avoid

1. Ignoring bleeding: Any postmenopausal bleeding requires evaluation regardless of endometrial thickness 1
2. Misinterpreting fluid: Intracavity fluid can falsely increase apparent endometrial thickness measurements 2
3. Overlooking risk factors: Women with risk factors may need evaluation even with borderline endometrial thickness 1, 4
4. Inadequate sampling: Office endometrial biopsies have approximately 10% false-negative rate; persistent symptoms warrant further evaluation 1

Evaluation Methods

When endometrial sampling is indicated:

• Transvaginal ultrasound (TVUS) is the first-line screening test 1
• Endometrial sampling devices (Pipelle) have high sensitivity (99.6%) for detecting endometrial carcinoma 1
• Hysteroscopy with directed biopsy is superior to blind sampling techniques for detecting focal lesions 1