Fig. 20. Example of the use of multiple progesterone levels for the diagnosis of luteal phase deficiency. This infertility patient had three serum progesterone levels drawn on days 6, 7, and 8 of her luteal phase. The day of the luteinizing hormone surge was identified by a urine luteinizing hormone test (day 0). The level varied from 8 to 15 ng/mL. The sum of the three progesterone levels was 34 ng/mL, which indicated normal corpus luteum function.