When to worry about the endometrial thickness in postmenopausal women?

Postmenopausal patients who present with vaginal bleeding should undergo transvaginal US.

Endometrial thickness >5 mm in postmenopausal women not receiving hormone replacement therapy is abnormal

Endometrial thickness >8 mm in patients receiving hormone replacement therapy or tamoxifen therapy) is abnormal (1).

If Transvaginal ultrasonography images reveal a thin endometrial echo (less than or equal to 4 mm), on initial evaluation of postmenopausal bleeding, it is usually sufficient to stop investigation, given that an endometrial thickness of 4 mm or less has a greater than 99% negative predictive value for endometrial cancer (2).

A thin, distinct echo - less than or equal to 4 mm in an average-risk woman, or less than 3 mm in virtually any woman.  excludes significant tissue. 

Reference:

1. Gupta A, Desai A, Bhatt S. Imaging of the Endometrium: Physiologic Changes and Diseases: Women's Imaging. Radiographics. 2017 Nov-Dec;37(7):2206-2207. doi: 10.1148/rg.2017170008. PMID: 29131769.

2. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2018/05/the-role-of-transvaginal-ultrasonography-in-evaluating-the-endometrium-of-women-with-postmenopausal-bleeding