Fetal adrenal cortical growth involves several cellular processes: hypertrophy, hyperplasia, apoptosis, and migration.In the second and third trimesters a steroid precursor dehydroepiandrosterone (DHEA) and sulphated derivative (DHEAS) which is converted by placenta into estrogen.Three functional zones:Fetal zone - throughout gestation expresses enzymes required for DHEA-S synthesis.Transitional zone - initially identical to the fetal zone but later (after 25-30 weeks) expresses enzymes that suggest glucocorticoid synthesis.Definitive zone - after 22-24 weeks expresses enzymes that suggest mineralocorticoid synthesis.