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
The endometrium is a dynamic tissue that changes throughout the menstrual cycle:
- Follicular phase: Typically thinner, with mean thickness around 0.6 cm (6 mm) 2
- Luteal phase: Significantly thicker, with mean thickness around 1.0 cm (10 mm) 2
- Overall range: 3-13 mm depending on cycle phase 1
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
For postmenopausal women, endometrial thickness guidelines are more clearly defined:
- ≤4 mm: Considered normal with a negative predictive value for endometrial cancer of nearly 100% 1
- >4 mm with bleeding: Requires further evaluation with endometrial sampling 1
- >11 mm without bleeding: Should prompt consideration of biopsy as the risk of cancer is approximately 6.7% 3
Clinical Implications
When evaluating endometrial thickness, several factors should be considered:
- Menopausal status: The most important determinant of normal range
- Symptoms: Presence or absence of vaginal bleeding significantly affects the clinical significance of endometrial thickness
- Hormone use: Women on hormone replacement therapy or tamoxifen may have different thresholds for normal endometrial thickness 4
Pitfalls to Avoid
- Relying solely on endometrial thickness without considering clinical context
- Failing to correlate thickness with the phase of menstrual cycle in premenopausal women
- Not recognizing that even with a thin endometrium (<4mm), persistent bleeding requires further evaluation 1
Transvaginal ultrasound is the first-line imaging modality for assessing endometrial thickness 1, with MRI serving as a complementary tool when ultrasound visualization is inadequate or for better soft tissue characterization.