Soru

A $32$-year-old woman is evaluated in the clinic for a $2$-year history of inability to conceive. She has never been pregnant. She and her partner have been engaging in frequent, unprotected intercourse. Over the past $18$ months, her menstrual cycles have lengthened to $45$ to $60$ days, and she has noticed increased dark hair growth on her upper lip and chin, requiring her to shave twice a week. She also reports a $12\text{-kg}$ ($26\text{-lb}$) weight gain during this period, predominantly in her abdominal area, and says she feels profoundly weak when trying to climb the stairs to her apartment. She takes a daily multivitamin. Vital signs show a blood pressure of $154/96 \text{ mm Hg}$, pulse of $82\text{/min}$, and BMI of $33 \text{ kg/m}^2$. Physical examination reveals a rounded, plethoric face and broad, violaceous stretch marks over the lower abdomen. Pelvic examination is unremarkable. Pelvic ultrasonography demonstrates bilaterally enlarged ovaries with multiple peripherally oriented small cysts. Which of the following is the most appropriate initial diagnostic step to ascertain the underlying cause of this patient's ovulatory dysfunction?