Circadian rhythms in maternal plasma cortisol, estrone, estradiol, and estriol at 34 to 35 weeks' gestation.

In order to examine the relationship between circadian rhythms in different steroids, cortisol (F), estrone E1), estradiol (E2), and estriol (E3) were measured by radioimmunoassay in maternal venous plasma taken at 30 to 60-minute intervals over 24 hours from 11 healthy women at 34 to 35 weeks' gestation. Maternal F was maximal at 0730 hours and fell significantly to its lowest concentration at 0230 hours. Maretnal E3 was lowest between 1000 and 1130 hours and rose significantly to maximal values between 2230 and 0030 hours. Maternal E1 was maximal between 1000 and 1130 hours and showed a significant decrease to reach its lowest concentration at 0430 to 0630 hours. No significant circadian change was measured in uncorrected concentrations of E2. We conclude that there is an inverse relationship between maternal F and E3, which would be consistent with a maternal effect on fetal adrenal function, and the existence of circadian rhythms in F, E1, E2, and E3 must be taken into account in clinical investigations of these hormones during pregnancy.