Ovulation
Throughout your menstrual cycle, your progesterone levels fluctuate, according to Net Doctor. A woman should reach her highest point of progesterone around seven days before she starts her period---a point also known as ovulation. At this point, a woman's progesterone level may reach up to 20 ng/mL, according to Natural Hormones. If a woman's progesterone levels are not high at this time or do not fluctuate at all, she may have a difficult time getting pregnant. If you are trying to get pregnant, a physician may measure your progesterone levels to ensure they are fluctuating enough in order for fertilization to take place.