What is the normal endometrial thickness?

Normal Endometrial Thickness

Normal endometrial thickness varies by menopausal status, with postmenopausal women having a threshold of ≤4 mm considered normal, while premenopausal women have variable thickness depending on menstrual cycle phase, typically ranging from 3-13 mm. 1

Premenopausal Women

Endometrial thickness in premenopausal women varies throughout the menstrual cycle:

• Follicular phase: 3-13 mm (mean 7.8 ± 2.1 mm) 2
• Around ovulation: 8-13 mm (mean 10.4 ± 1.9 mm) 2
• Luteal phase: 8-19 mm (mean 10.4 ± 2.3 mm) 2

It's important to note that there is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women, and endometrial thickness alone is not a reliable indicator of endometrial pathology in this population 1.

Postmenopausal Women

• Normal thickness: ≤4 mm 1
• Average thickness without bleeding: 1.4 ± 0.7 mm (range 1-5 mm) 2

An endometrial thickness ≤4 mm in postmenopausal women has a negative predictive value for endometrial cancer of nearly 100% 1. This threshold is particularly important in the evaluation of postmenopausal bleeding, where endometrial thickness >4 mm requires further evaluation with endometrial sampling 1.

Clinical Implications

Postmenopausal Women

• Endometrial thickness >4 mm in postmenopausal women warrants further investigation, especially in those with vaginal bleeding 1, 3
• In a study of postmenopausal women with bleeding, all cases of endometrial cancer had an endometrial thickness ≥12 mm 4
• Some studies suggest even lower thresholds may be appropriate, with one study finding that a cutoff of 2.8 mm had the best negative likelihood ratio for excluding focal intrauterine pathology in asymptomatic postmenopausal women 5

Pathological Findings

When endometrial thickness is increased, various pathologies may be present:

• Atrophic endometrium: mean thickness 2.2 ± 2.0 mm 2
• Endometrial hyperplasia: mean thickness 17.4 ± 6.7 mm 2
• Endometrial polyps: mean thickness 16.7 ± 7.7 mm 2
• Endometrial carcinoma: mean thickness 24.4 ± 11.9 mm 2

Pitfalls and Caveats

1. Fluid collections: Intracavitary fluid can falsely increase the apparent endometrial thickness measurement 3. Always evaluate for the presence of fluid when measuring endometrial thickness.

2. Asymptomatic vs. symptomatic: The 4 mm threshold commonly used for postmenopausal women with bleeding may not be directly transferable to asymptomatic women 5.

3. Measurement technique: Endometrial thickness should be measured in the longitudinal plane at the thickest part, including both anterior and posterior layers.

4. Risk factors: When interpreting endometrial thickness, consider other risk factors that increase concern with thickened endometrium, including obesity, diabetes mellitus, hypertension, history of unopposed estrogen exposure, and tamoxifen therapy 1.

5. Volume vs. thickness: Some research suggests that endometrial volume measurement may be superior to thickness measurement for detecting endometrial cancer in symptomatic postmenopausal women 6.