Steroid hormones are essential for maintenance of pregnancy and fetal development. The expression and catalytic activity of the key steroidogenic enzymes involved in the production of progesterone and estrogens increase during pregnancy, and there is an intricate communication between the mother, the placenta, and the fetus in order to maintain a balanced supply of the steroid hormones essential for embryogenesis. This chapter describes methods for the measurement of the expression and catalytic activity of three key cytochrome P450 (CYP) enzymes involved in the production of progesterone and estrogens, aromatase (CYP19), steroid 17α-hydroxylase/17,20-lyase (CYP17), and cholesterol side-chain cleavage (CYP11A).
