**Core Concept:** Evaluation of postmenopausal bleeding involves assessing the cause and determining the appropriate management strategy. It is essential to differentiate between natural menopause-related bleeding and abnormal bleeding due to various underlying conditions.

**Why the Correct Answer is Right:**
Correct Answer: **B. Transvaginal ultrasound (TVUS)**

In postmenopausal women, transvaginal ultrasound (TVUS) is the first-line investigation to evaluate endometrial thickness, morphology, and vascularity. TVUS provides non-invasive, accurate, and rapid evaluation of the endometrial structure, helping to differentiate between normal postmenopausal bleeding (resulting from hormonal changes) and abnormal bleeding due to endometrial pathology, such as endometrial hyperplasia or cancer.

**Why Each Wrong Option is Incorrect:**
A. **Transabdominal ultrasound (TAUS):** TAUS is less sensitive and specific than TVUS for evaluating the endometrium. It is less accurate due to limited visualization of the endometrium and the impact of bladder fullness on assessment.
C. **Blood tests (Hormone levels):** Although hormonal evaluations can provide information on overall hormonal levels, they do not directly assess the endometrium or differentiate between natural postmenopausal bleeding and abnormal bleeding.
D. **Endometrial biopsy:** Endometrial biopsy is an invasive procedure, and it should be reserved for cases where initial ultrasound evaluation is inconclusive or suspicious for endometrial pathology.

**Clinical Pearl:** In postmenopausal women presenting with vaginal bleeding, TVUS is the initial investigation of choice to evaluate endometrial thickness, morphology, and vascularity. This helps differentiate between natural postmenopausal bleeding and abnormal bleeding due to endometrial pathology, guiding further management decisions and minimizing the need for unnecessary invasive procedures like endometrial biopsy.