What does an endometrial thickness of 6.6 mm indicate?

Interpreting an Endometrial Thickness of 6.6 mm

An endometrial thickness of 6.6 mm requires different clinical interpretation and management depending on menopausal status, with greater concern for pathology in postmenopausal women than in premenopausal women where this measurement may be normal. 1

Interpretation Based on Menopausal Status

Postmenopausal Women:

• In postmenopausal women, an endometrial thickness of 6.6 mm exceeds the 5 mm threshold that generally prompts endometrial tissue sampling, as it may indicate underlying pathology 1
• An endometrial thickness ≥5 mm in postmenopausal women has been associated with endometrial hyperplasia, polyps, or malignancy 1
• The negative predictive value for cancer approaches 100% when the endometrium measures ≤4 mm in postmenopausal women, but risk increases with greater thickness 1
• At 6.6 mm, the risk of pathology is significant enough to warrant further evaluation, especially if the patient has postmenopausal bleeding 2

Premenopausal Women:

• In premenopausal women, an endometrial thickness of 6.6 mm may be entirely normal depending on the phase of the menstrual cycle 1
• There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women 1
• Normal endometrial thickness varies throughout the menstrual cycle in premenopausal women, making the 6.6 mm measurement less concerning than in postmenopausal women 1

Clinical Management Algorithm

For Postmenopausal Women:

1. If patient has vaginal bleeding:

   • Endometrial sampling is recommended as 6.6 mm exceeds the 5 mm threshold 1
   • Risk of endometrial cancer is approximately 7.3% when endometrium is >5 mm with bleeding 3

2. If patient does not have vaginal bleeding:

   • At 6.6 mm, the risk is lower than with bleeding but still warrants consideration of further evaluation 3
   • Studies suggest that in asymptomatic postmenopausal women, even thresholds between 3.0-5.9 mm are associated with increased risk of endometrial pathology (relative risk 5.08) 4

For Premenopausal Women:

1. Consider menstrual cycle phase:

   • Endometrial thickness normally varies with cycle phase 1
   • Even with thin endometrium (<5 mm), pathology may still be present in premenopausal women 1

2. Evaluate for abnormal echogenicity or texture:

   • Abnormal echogenicity and texture of the endometrium correlates with underlying uterine pathology regardless of thickness 1
   • Consider sonohysterography if focal abnormality is suspected 1

Important Considerations

• Transvaginal ultrasound approach: For optimal assessment, transvaginal ultrasound should be combined with transabdominal ultrasound to fully evaluate pelvic structures 1

• Doppler evaluation: Color and spectral Doppler should be used to evaluate internal vascularity, which can help identify vessels within endometrial polyps or cancer 1

• Limitations of measurement alone: While endometrial thickness measurement is sensitive, it cannot reliably determine the etiology of endometrial thickening 1

• Additional imaging: If initial ultrasound findings are inconclusive, sonohysterography may be considered to further characterize endometrial abnormalities 1

Risk Stratification

• Studies suggest that endometrial thickness between 6.0-9.9 mm in asymptomatic postmenopausal women carries a relative risk of 4.34 for atypical endometrial hyperplasia or endometrial carcinoma 4

• The diagnostic accuracy of endometrial thickness measurement shows decreasing sensitivity but increasing specificity as the threshold increases 4