Twenty-four-hour pattern of cortisol in the human fetus at term

OBJECTIVES: Indirect evidence suggests that adrenal steroid production in t he human fetus may have a circadian rhythm. To assess whether there is a 24 -hour rhythm of fetal cortisol in the human fetus, we investigated the rela tionship between fetal and maternal cortisol and cortisone concentrations i n maternal, umbilical arterial, and umbilical venous blood samples over a 2 4-hour period. STUDY DESIGN: Elective cesarean sections were scheduled every 2 hours aroun d the clock in 57 term (38-41 weeks' gestation) nonlaboring pregnant women. Plasma cortisol and cortisone concentrations were measured by high-pressur e liquid chromatography. RESULTS: The mean 24-hour cortisol concentration was higher In umbilical ar terial than in umbilical Venous blood samples. 63.6 +/- 4.6 ng/mL (SEM) ver sus 48.7 +/- 3.2 ng/mL, respectively (P <.05). Fetal plasma cortisol showed a rhythm in the umbilical artery (acme from noon to 4 PM) (I-way analysis of variance and least significant difference test; P <.05) but not in the u mbilical vein. Umbilical arteriovenous differences showed no net transfer o f cortisol to the fetus at any time of the day and net fetal production of cortisol from 8 AM to 6 PM. There was limited transfer of cortisone to the fetus and only in the 2 AM-to-noon time interval. CONCLUSION: These data suggest the presence of a 24-hour rhythm of fetal ad renal cortisol secretion that may be controlled by a fetal circadian pacema ker.