**Core Concept:**
Ovarian reserve refers to the number and quality of ovarian follicles in a woman's ovaries, which are essential for egg production and menstrual cycles. Testing ovarian reserve helps in assessing a woman's fertility potential and guiding treatment decisions.

**Why the Correct Answer is Right:**
The correct answer is measuring Anti-Müllerian Hormone (AMH). AMH is a hormone produced by granulosa cells of small antral follicles in the ovaries. Its level in blood decreases as the number of follicles decreases, making it a reliable marker of ovarian reserve. AMH levels are significantly higher in women with higher ovarian reserve and lower in those with diminished ovarian reserve.

**Why Each Wrong Option is Incorrect:**

A. **Anti-Müllerian Receptor Antibody (AMRA)** is an antibody that binds to AMH, but it is not used clinically for measuring ovarian reserve.

B. **Anti-Müllerian Receptor Antibody (AMRA)**: Similar to option A, this is an antibody that binds to AMH but is not used in clinical practice for evaluating ovarian reserve.

C. **Anti-Müllerian Receptor Antibody (AMRA)**: As mentioned earlier, this is an antibody binding to AMH, not used for ovarian reserve assessment.

D. **Anti-Müllerian Receptor Antibody (AMRA)**: As mentioned above, this is an antibody binding to AMH but is not used in measuring ovarian reserve.

**Clinical Pearl:**
AMH testing is a reliable marker for ovarian reserve assessment in women of reproductive age, particularly during cycles prior to in vitro fertilization (IVF) treatment. Monitoring AMH levels can guide treatment decisions and prognosis.