CONTEXT: The endocrine function of human fetal adrenals (HFAs) is activated already during first trimester, but adrenal steroidogenesis during fetal life is not well characterized.

OBJECTIVE: This study aimed to investigate HFA steroidogenesis by analyzing adrenal glands from first and second trimesters.

DESIGN AND SETTING: Male and female HFA from gestational weeks (GWs) 8 to 19 were examined, including a total of 101 samples from 83 fetuses.

MAIN OUTCOME MEASURE(S): Expression level of steroidogenic genes and protein expression/localization were determined by quantitative PCR and immunohistochemistry, respectively, and intra-adrenal steroid levels were quantified by LC-MS/MS.

RESULTS: Transcriptional levels of StAR, CYP11A1, CYP17A1, CYP21A2, CYP11B1/2, and SULT2A1 were significantly higher in second trimester compared to first trimester (P < 0.05), whereas expression levels of 3β-HSD2 and ARK1C3 were unaltered between GWs 8 and 19. All investigated steroidogenic proteins were expressed in a distinct pattern throughout the investigated period, with most enzymes expressed primarily in the fetal zone, except 3β-HSD1/2, which was expressed mainly in the definitive zone. Abundant steroidogenic enzyme expression was reflected in overall high intra-adrenal tissue concentrations of mineralocorticoids, glucocorticoids, and androgens; cortisol was the most abundant (1071 to 2723 ng/g tissue), and testosterone levels were the lowest (2 to 14 ng/g tissue).

CONCLUSIONS: The expression profiles of HFA steroidogenic enzymes are distinct from first to second trimester, with no major differences between male and female samples. Intra-adrenal steroid hormone concentrations confirm that cortisol is produced throughout first and second trimesters, suggesting continued regulation of the hypothalamus-pituitary-adrenal axis during this entire period.