Normal Uterine Thickness
The 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
Endometrial Thickness by Menopausal Status
Postmenopausal Women
- Endometrial thickness ≤4 mm is considered normal 1
- This threshold has a negative predictive value for endometrial cancer of nearly 100% 1
- For asymptomatic postmenopausal women without vaginal bleeding, a higher threshold of ≤11 mm may be appropriate before biopsy is indicated 2
- Endometrial thickness can correlate with body weight in postmenopausal women - women with higher BMI tend to have thicker endometria 3
Premenopausal Women
- Normal range typically varies from 3-13 mm depending on menstrual cycle phase 1
- Early follicular phase: thinner endometrium
- Late secretory/proliferative phase: thicker endometrium
- There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women 1
- In premenopausal women with abnormal uterine bleeding, an endometrial thickness of ≤8 mm has been suggested as a threshold with good negative predictive value (90.4%) for abnormal pathology 4
Myometrial Thickness
The myometrium (uterine muscle layer) thickness is not as well standardized in guidelines as endometrial thickness. However, some key points:
- Normal myometrial thickness in the non-pregnant uterus is typically several centimeters
- During pregnancy, the myometrium gradually thins as the uterus expands
- Reduced myometrial thickness of <1 cm can be a concerning finding in pregnancy, particularly when evaluating for placenta accreta spectrum disorders 5
- The normal non-pregnant uterus is described as "small and firm" in physical examination 5
Clinical Implications
- Endometrial thickness measurement by transvaginal ultrasound is the first-line screening test for endometrial pathology 1
- A combined transabdominal and transvaginal approach provides optimal assessment of pelvic structures 1
- Endometrial thickness alone should not be the only parameter evaluated - abnormal echogenicity and texture also correlate with significant underlying uterine pathology 1
- In women without abnormal uterine bleeding, transvaginal measurement of endometrial thickness is most useful for excluding focal intrauterine pathology, especially in postmenopausal women 6
Important Considerations
Endometrial thickness measurements should be interpreted in clinical context, including:
- Menopausal status
- Presence or absence of abnormal uterine bleeding
- Use of hormone therapy
- Body mass index
- Other risk factors for endometrial pathology
When endometrial thickness exceeds normal thresholds, further evaluation with endometrial sampling is typically indicated 1
For premenopausal women, the phase of menstrual cycle must be considered when interpreting endometrial thickness measurements