progesterone

(prō-jĕsˈtə-rōnˌ)

1. A steroid hormone, C₂₁H₃₀O₂, secreted by the corpus luteum of the ovary and by the placenta, that acts to prepare the uterus for implantation of the fertilized ovum, to maintain pregnancy, and to promote development of the mammary glands.
2. A drug prepared from natural or synthetic progesterone, used in the prevention of miscarriage, in the treatment of menstrual disorders, and as a constituent of some oral contraceptives.