Placental steroid hormone synthesis: unique features and unanswered questions.

Despite the amazing diversity of placental architecture across species, a number of common elements can be found, including the ability of all placentae to synthesize and metabolize steroid hormones; the assignment of steroidogenic activities to specific trophoblast phenotypes; the use of novel mechanisms to control expression of steroidogenic enzyme genes, which differ from those employed in the adrenal cortex and gonads; and interactions with the maternal and fetal compartments encompassing supply of steroid hormone precursors as well as regulatory influences of maternal ovarian and pituitary hormones and fetal adrenal cortical steroids.