CIRCADIAN VARIATIONS IN PLASMA PROGESTERONE IN THE LUTEAL PHASE OF THE MENSTRUAL CYCLE AND DURING PREGNANCY

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Abstract
To investigate possible variations in plasma progesterone levels during the hyperthermic phase of the menstrual cycle and during early and late pregnancy, venous blood samples were taken at 4-hour intervals during periods of 24 hours. Progestrone determinations were done by gas-liquid chromatography. No significant circadian variation in peripheral plasma progesterone concentration was determined in the 10 women studied during the hyperthermic phase of their menstrual cycles or in 14 women studied during early pregnancy. However in the 15 women studied in late pregnancy a statistically significant rise was found from 8 a.m. until 4 or 8 p.m. (p less than .001), followed by a decrease until 4 to 8 a.m. Results indicate a daily change in peripheral plasma progesterone level during the last trimester of pregnancy. The cause of this diurnal variation is not known.

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