title: Variations in urinary levels of free 6 beta-hydroxycortisol, cortisol, and estrogens in late pregnancy.
abstract: The urinary excretion of 6 beta-hydroxycortisol (6 beta-OHF), free cortisol, and estriol was studied at 4-hourly intervals in 9 subjects between the 36th and 38th week of pregnancy. The ratio of 6 beta-OHF to creatinine showed a significant diurnal rhythm with a 40% fall from a peak at 06.00-10.00 h to a trough at 22.00-02.00 h. There was a significant positive correlation between the excretion of 6 beta-OHF and free cortisol. Estrogen excretion showed no diurnal variation. No increase was observed in the 6 beta-OHF:creatinine ratio in early morning urine samples from 5 subjects followed daily prior to the onset of spontaneous labour at term. Normal nonpregnant females were also found to excrete significant quantities of 6 beta-OHF. These findings suggest that the clinical significance of 6 beta-OHF levels measured in a single void sample of urine has to be reassessed in the face of such a marked diurnal variation.
mesh_terms: D002940:Circadian Rhythm; D004967:Estrogens / Q000652:urine*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000031:analogs & derivatives* / Q000652:urine*; D007752:Obstetric Labor, Premature / Q000175:diagnosis / Q000652:urine; D011247:Pregnancy; D011263:Pregnancy Trimester, Third
chemical_list: D004967:Estrogens; C001380:6 beta-hydroxycortisol; D006854:Hydrocortisone