Progesterone is a steroid hormone. In animals, it is made from cholesterol. It is the base for making certain estrogens and androgens. In animals, it is produced by their body mainly during the second half of the menstrual cycle. During pregnancy it is produced in higher quantities. Willard Myron Allen co-discovered progesterone with his anatomy professor George Washington Corner at the University of Rochester Medical School in 1933 year. Allen discovered temperature needed to melt it and its weight. He also gave it the name Progesterone based on Progestational Steroidal ketone. In one plant, Juglans regia, progesterone has been found. Also progesterone-like steroids are found in Dioscorea mexicana. Progesterone level is very low in children and postmenopausal women.