Progestagens (also spelled progestogens or gestagens) are a group of hormones including progesterone. The progestagens are one of the five major classes of steroid hormones, in addition to the estrogens, androgens, mineralocorticoids, and glucocorticoids. All progestagens are characterized by their basic 21 carbon skeleton, called a pregnane skeleton (C21). Similarly, the estrogens possess an estrane skeleton (C18) and androgens, an andrane skeleton (C19). Progestagens are named for their fun… (More on Progestagens)