Plasma levels of progesterone in pregnancy measured by a rapid competitive protein binding technique

Plasma levels of progesterone* were measured during normal human pregnancy by a sensitive and rapid competitive protein binding technique. During the first half of gestation 440 determinations in 321 women and in the second half of gestation, 209 determinations in 160 women were performed. The average plasma level of progesterone in the 5th week of gestation was 24.8 ± 7.3 (s) ng/ml which is above the normal range of the luteal plateau of the menstrual cycle (10–20 ng/ml). Between the 5th and the 9th week of gestation the plasma concentration decreased significantly. From the 9th to the 32nd week of gestation the plasma level of progesterone increased from 16.7 ± 7.4 (s) to 125.2 ± 37.9 (s) ng/ml. During the last 8 weeks of gestation the plasma levels of progesterone did not show any significant rise. One woman was followed up from the day of ovulation to the 8th week of gestation. An increase in progesterone levels was observed about 10 days after ovulation. Morning samples of progesterone, which were taken before the 20th week of gestation, when the woman was still in bed, were found to be somewhat higher than levels found during the remainder of the day. Progesterone concentrations in a few abnormal pregnancies are also reported.