PdG is the urine metabolite of progesterone. Progesterone is the hormone produced by the empty follicle (corpus luteum) after an egg has been released. Progesterone prepares the uterus for embryo implantation. Without enough progesterone, implantation can not occur. After circulating through the blood, progesterone is metabolized by the kidneys into PdG, which is expelled from the body in urine and can be detected by the Proov test kit.