Pregnenolone serves as a principal precursor to all the other steroid hormones synthesized by the ovary, testes, or adrenals. It shows that the rate-limiting step for the production of progesterone is side-chain cleavage of cholesterol by P450scc. Pregnenolone is then converted into progesterone by 3β-hydroxysteroid dehydrogenase (3β-HSD). The deficiencies in either P450scc or 3β-HSD have ardent effects on the synthesis of all steroids. In the ovary, progesterone is produced at all stages of follicular development as an intermediate for androgen and estrogen synthesis but becomes a primary secretory product during the peri- and postovulatory (luteal) phases. The synthesis of progesterone is controlled by FSH during the early stages of folliculogenesis
