Which diagnostic test is NOT commonly used for amenorrhea?

The diagnostic test that is not commonly used for amenorrhea is MRI of the pelvis. In clinical practice, the evaluation of amenorrhea typically starts with more conventional tests that can effectively identify the common causes without requiring more invasive imaging techniques.

Serum prolactin levels, pregnancy tests, and serum TSH (thyroid-stimulating hormone) tests are all standard initial assessments. Prolactin levels help evaluate potential pituitary abnormalities, while a pregnancy test rules out the most common cause of secondary amenorrhea. Serum TSH is important for assessing thyroid function, as thyroid disorders can significantly impact menstrual cycles.

In contrast, an MRI of the pelvis is generally not one of the first-line tests for amenorrhea. It may be reserved for specific situations where there's a suspicion of structural abnormalities within the reproductive organs or the pituitary gland, but it is not routinely used due to its cost, availability, and the need for specialized imaging interpretation. Thus, it does not fit into the common diagnostic procedures typically employed in the initial assessment of amenorrhea.