What is a normal endometrial thickness?

Normal Endometrial Thickness

Normal endometrial thickness varies dramatically based on menopausal status: in postmenopausal women, the endometrium should measure ≤4 mm, while in premenopausal women, thickness varies with menstrual cycle phase and is not a reliable indicator of pathology. 1

Postmenopausal Women

The critical threshold for postmenopausal women is ≤4 mm, which conveys a negative predictive value for endometrial cancer of nearly 100%. 1, 2

• An endometrial thickness of ≤4 mm in postmenopausal women effectively excludes endometrial malignancy and requires no further evaluation if the patient is asymptomatic 1, 2
• When endometrial thickness measures ≥5 mm in postmenopausal women, endometrial tissue sampling is generally warranted 1, 2
• Research data supports these thresholds, showing mean endometrial thickness in asymptomatic postmenopausal women of 2.9 mm (95% CI, 2.6-3.3 mm) 3
• The European Society for Medical Oncology uses a slightly more conservative cut-off of 3-4 mm 1, 2

Important Clinical Context for Postmenopausal Women

• Transvaginal ultrasound (TVUS) is the first-line screening test for evaluating endometrial thickness in postmenopausal women, particularly those with bleeding 1, 2
• TVUS should be combined with transabdominal ultrasound whenever possible for complete pelvic assessment 1, 2
• While TVUS is highly sensitive for measuring endometrial thickness, it cannot reliably determine the etiology of endometrial thickening 1

Premenopausal Women

In premenopausal women, endometrial thickness varies significantly with menstrual cycle phase and is NOT a reliable indicator of endometrial pathology. 1

• Follicular phase: Mean thickness of 7.8 ± 2.1 mm (range 3-13 mm) 4
• Around ovulation: Mean thickness of 10.4 ± 1.9 mm (range 8-13 mm) 4
• Luteal phase: Mean thickness of 10.4 ± 2.3 mm (range 8-19 mm) 4

Critical Pitfall in Premenopausal Women

• Even if endometrial thickness is <5 mm in premenopausal women, endometrial polyps or other pathology may still be present 1
• Endometrial thickness measurement has limited diagnostic value in premenopausal women and should not be used to exclude pathology 1
• Clinical symptoms (such as abnormal uterine bleeding) rather than thickness measurements should guide the decision for endometrial sampling in premenopausal women 1

Asymptomatic Postmenopausal Women: Special Considerations

• For asymptomatic postmenopausal women, an endometrial thickness threshold of ≤11 mm has been proposed, above which tissue sampling should be considered to rule out hyperplasia or malignancy 5
• However, screening asymptomatic postmenopausal women with endometrial thickness measurement is not justified, as sensitivity and specificity are insufficient for screening purposes 3
• The prevalence of endometrial carcinoma in asymptomatic postmenopausal women is only 0.62% (95% CI, 0.42-0.82%) 3

Pregnancy of Unknown Location Context

• In early pregnancy evaluation, an endometrial thickness <8 mm virtually excludes normal intrauterine pregnancy 1
• An endometrial thickness of ≥25 mm virtually excludes ectopic pregnancy (present in only 4 cases in one study) 1