(biochemistry) C21H31.1O2 Steroid sex hormone secreted by the corpus lutcum of the mammalian ovary, placenta, tcstcs and adrenal cortex. In females it prepares the uterus for the implantation of a fertilised ovum (egg) and during pregnancy maintains nourishment for the embryo by developing the placenta, inhibiting ovulation and menstruation, and stimulating the growth of the mammary glands.
