A 28 yo nulligravid woman stopped taking OCPs 1 year ago with the goal of pregnancy. However, she never resumed spontaneous menstrual cycles. Her PCP ordered tests showing FSH level of 45 mIU/mL, estradiol level of 12 pg/mL, TSH of 1.37 mIU/mL and prolactin of 9 ng/mL. The most appropriate next test to screen her evaluation is: