Plasma progesterone, 17a-OH-progesterone , estrone, 17(3-estradiol and estriol in human normal pregnancy, labor and the puerperium were measured simultaneously with radioimmunoassay or competitive protein binding assay . The steroids were extracted from the sample plasma with diethyl ether , and were separated through two steps of sephadex LH-20 microcolumn chromatography prior to the assays . From the beginning to the 25th week of pregnancy , a gradualrise in the levels of plasma progesterone

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... as noted, followed by a steep increasetoward term with a level of 150-250 ng/ml at the end of gestation . The levels of 17a-OH-progesterone during the 7 th or 8 th week of pregnancy were 2-3 ng/ml, which was above the normal range in the luteal phase , followed by a gradual decrease during 15-25 weeks of gestation . Thereafter, an increase toward term was seen with a mean level of 6-10 ng/ml in the 40th week .