A

Endometrial thickness ≥ 5 mm on an initial trans-abdominal scan is the usual cut-off that triggers a more sensitive evaluation with trans-vaginal sonography in post-menopausal bleeding, because thickness below this level is rarely associated with malignancy, whereas values ≥5 mm warrant closer assessment [Nasri 1991, PMID 12797060; Bennett 2011, PMID 21723482].