Normal Endometrial Thickness
Normal endometrial thickness varies significantly based on menopausal status: in postmenopausal women, the endometrium should measure ≤4 mm (with values ≤5 mm considered acceptable in asymptomatic women), while in premenopausal women, thickness varies throughout the menstrual cycle from approximately 3-8 mm in the follicular phase to 8-19 mm in the luteal phase. 1, 2, 3, 4
Postmenopausal Women
For postmenopausal women not on hormone replacement therapy:
- The mean endometrial thickness is approximately 2.9 mm (95% CI, 2.6-3.3 mm) 5
- An endometrium measuring ≤4 mm has a negative predictive value approaching 100% for excluding endometrial cancer 1, 3
- The generally accepted upper limit is ≤5 mm in asymptomatic postmenopausal women 3, 4
- Any measurement >5 mm warrants endometrial tissue sampling, particularly in symptomatic women with postmenopausal bleeding 2, 3
- Measurements ≥11 mm in asymptomatic postmenopausal women are considered significantly abnormal and require tissue sampling 2
Premenopausal Women
Endometrial thickness in premenopausal women varies cyclically and depends on menstrual phase:
- Follicular phase (early cycle): 7.8 ± 2.1 mm (range 3-13 mm) 4
- Periovulatory period: 10.4 ± 1.9 mm (range 8-13 mm) 4
- Luteal phase (late cycle): 10.4 ± 2.3 mm (range 8-19 mm) 4
- There is no validated absolute upper limit cutoff for endometrial thickness in premenopausal women, as normal variation is substantial 3
Important Clinical Caveats
When interpreting endometrial thickness measurements:
- Measurement technique matters: use transvaginal ultrasound for optimal visualization, measuring the maximum anterior-posterior diameter of the endometrial stripe 1, 3
- Endometrial thickness alone cannot determine the etiology of thickening—tissue sampling is required for definitive diagnosis when abnormal 3
- Abnormal echogenicity and texture correlate with underlying pathology regardless of absolute thickness 3
- In postmenopausal women with bleeding, even measurements between 4-5 mm may warrant investigation depending on clinical context 1, 6
- Color Doppler evaluation of internal vascularity can help identify abnormal vascular patterns suggestive of pathology 2, 3