Progesterone levels in the blood during the menstrual cycle

Progesterone levels vary considerably throughout the menstrual cycle, peaking about a week after ovulation in the absence of fertilization. If the oozyte is not fertilized and implanted in the uterine lining, progesterone levels fall, triggering menstruation. (Source: Häggström M. Reference ranges for estradiol, progesterone, luteinizing hormone and follicle-stimulating hormone during the menstrual cycle. Mikael Wikiversity J Med 2014;1(1). Courtesy of Wikimedia Commons. Public domain.)