What is the normal endometrial thickness?

Normal Endometrial Thickness

The normal endometrial thickness is ≤4 mm in postmenopausal women, while in premenopausal women it varies with the menstrual cycle, ranging from 3-13 mm in the follicular phase, 8-13 mm around ovulation, and 8-19 mm in the luteal phase. 1, 2

Endometrial Thickness by Menopausal Status

Postmenopausal Women

• ≤4 mm is considered normal 1
• Thickness ≤4 mm has a negative predictive value for endometrial cancer of nearly 100% 1
• Thickness ≥5 mm generally requires further evaluation, especially with vaginal bleeding 1
• The average thickness in asymptomatic postmenopausal women is approximately 1.4 ± 0.7 mm (range 1-5 mm) 2

Premenopausal Women

• Normal thickness varies throughout the menstrual cycle:
  • Follicular phase: 7.8 ± 2.1 mm (range 3-13 mm) 2
  • Around ovulation: 10.4 ± 1.9 mm (range 8-13 mm) 2
  • Luteal phase: 10.4 ± 2.3 mm (range 8-19 mm) 2
• No validated absolute upper limit exists for premenopausal women 1

Clinical Implications

When to Consider Endometrial Sampling

• Postmenopausal women:

  • Endometrial thickness ≥5 mm with or without bleeding 1
  • Endometrial thickness ≥11 mm in asymptomatic women 3
  • Any abnormal vaginal bleeding regardless of endometrial thickness 4, 1

• Premenopausal women:

  • Heavy or irregular menstrual bleeding in women over 35 years 1
  • Abnormal endometrial appearance on ultrasound 1

Diagnostic Accuracy

• Transvaginal ultrasound (TVUS) is the first-line screening test 1
• Endometrial sampling devices have high sensitivity:
  • Pipelle: 99.6% sensitivity for endometrial carcinoma 4, 1
  • Vabra: 97.1% sensitivity for endometrial carcinoma 4, 1

Important Considerations

Factors Affecting Endometrial Thickness

• Hormone replacement therapy can increase endometrial thickness 5
• Body weight correlates with endometrial thickness in postmenopausal women 6
• Higher BMI is associated with greater endometrial thickness 6

Pitfalls to Avoid

1. Don't rely solely on endometrial thickness in premenopausal women - interpretation must consider the phase of menstrual cycle
2. Don't dismiss postmenopausal bleeding with normal endometrial thickness - although rare, endometrial cancer can occur with endometrial thickness <5 mm
3. Don't overlook focal lesions - hysteroscopy with directed biopsy is superior to blind sampling techniques for detecting focal lesions 1
4. Don't ignore endometrial texture and echogenicity - abnormal patterns can indicate underlying pathology even with normal thickness 1

Risk Stratification

In asymptomatic postmenopausal women:

• Endometrial thickness >11 mm carries approximately 6.7% risk of cancer 3
• Endometrial thickness ≤11 mm carries approximately 0.002% risk of cancer 3
• Risk increases with age - from 4.1% at age 50 to 9.3% at age 79 with thickness >11 mm 3