CIRCADIAN VARIATIONS IN PLASMA PROGESTERONE IN THE LUTEAL PHASE OF THE MENSTRUAL CYCLE AND DURING PREGNANCY
ABSTRACT Serial plasma progesterone determinations were performed by gas-liquid chromatography in healthy women during 24 hour periods during the luteal phase of the cycle and during pregnancy. In 10 women during the hyperthermic phase of the cycle and in 14 women during early pregnancy (week 8–18) no significant circadian variation in the peripheral plasma progesterone concentration was observed. During later pregnancy (week 20–41) in 15 women, a statistically significant rise in the plasma progesterone concentration, usually from 8.00 a.m. until between 4.00 and 8.00 p. m. followed by a decrease after 8.00 p. m. until between 4.00 and 8.00 a. m., was demonstrated. The data indicate a diurnal change in the peripheral plasma progesterone level during the last trimester of pregnancy.