A 28-year-old woman with primary infertility for 2 years presents to the fertility clinic. Semen analysis of her husband is normal. Her menstrual cycles are regular (28 days), and transvaginal ultrasound shows normal ovaries with multiple follicles. Serum progesterone on day 21 of the cycle is 8 ng/mL (normal luteal phase >10 ng/mL). What is the most appropriate next step in management?