title: Twenty-four-hour pattern of cortisol in the human fetus at term.
abstract: OBJECTIVE
  Indirect evidence suggests that adrenal steroid production in the 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 relationship between fetal and maternal cortisol and cortisone concentrations in maternal, umbilical arterial, and umbilical venous blood samples over a 24-hour period.
  
  
  METHODS
  Elective cesarean sections were scheduled every 2 hours around the clock in 57 term (38-41 weeks' gestation) nonlaboring pregnant women. Plasma cortisol and cortisone concentrations were measured by high-pressure liquid chromatography.
  
  
  RESULTS
  The mean 24-hour cortisol concentration was higher in umbilical arterial than in umbilical venous blood samples, 63.6 +/- 4.6 ng/mL (SEM) versus 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 ) (1-way analysis of variance and least significant difference test; P <.05) but not in the umbilical vein. Umbilical arteriovenous differences showed no net transfer of 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.
  
  
  CONCLUSIONS
  These data suggest the presence of a 24-hour rhythm of fetal adrenal cortisol secretion that may be controlled by a fetal circadian pacemaker.
authors.affiliation: Unidad de Reproducción y Desarrollo, Facultad de Ciencas Biológicas, Santiago, Chile.
authors.forename: M
authors.initials: M
authors.lastname: Serón-Ferré
authors.forename: R
authors.initials: R
authors.lastname: Riffo
authors.forename: G J
authors.initials: GJ
authors.lastname: Valenzuela
authors.forename: A M
authors.initials: AM
authors.lastname: Germain
mesh_terms: D000328:Adult; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm; D003348:Cortisone / Q000097:blood; D036861:Delivery, Obstetric; D005260:Female; D005312:Fetal Blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D011247:Pregnancy
chemical_list: D003348:Cortisone; D006854:Hydrocortisone