Plasma Progesterone Levels in Normal and Abnormal Pregnancies

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Abstract
Plasma progesterone levels were estimated by competitive protein binding in 815 samples from healthy pregnant women with uncomplicated pregnancies. This series includes 32 patients who were followed serially throughout pregnancy. The mean level increased from 47 ng/ml in week 22 to 148 ng/ml in week 41. The spread was large. Individual patients showed very large variations between two consecutive weeks.Diurnal variations were examined in 7 patients and short‐time variations during one hour in 5 patients. Large but non‐systematic variations were found in most cases. The maximal difference between values observed over a 24‐hour‐period was 123 ng/ml and during one hour 150 ng/ml.Plasma progesterone levels were studied in 87 cases of toxemia of pregnancy, 6 cases of hypertension, 54 cases of Rh‐immunization, 37 cases of diabetes and 5 cases of fetal growth retardation of unknown origin. The results indicate that no constant changes occur in plasma progesterone levels in these groups or in cases of impending fetal death.As the normal limits are very wide, the intraindividual variations large, and the progesterone values in high risk pregnancies are inconclusive, plasma progesterone estimates during the latter part of pregnancy seem to be of limited value.During human pregnancy large amounts of progesterone are produced by the placenta (1, 14). The production rate during the third trimester lies between 200 and 300 mg/day (9). Part of the progesterone produced is metabolized to pregnanediol and excreted in the urine as the 3‐glucuronidate (16). The percentage of conversion to pregnanediol seems to vary with the stage of gestation and is influenced by pathological alterations in risk pregnancies (2, 5).Large day to day variations in the urinary pregnanediol levels have been found. It is thus hardly surprising that the clinical value of serial determinations of urinary pregnanediol in late pregnancy has been limited.Recently useful methods for the assay of progesterone in plasma have been developed and applied to physiological and clinical studies. A number of reports dealing with the prognostic value of progesterone determinations in complicated pregnancies have been published (8, 12, 17). The number of cases investigated is, however, small and the results are, in many respects, inconclusive. The aim of the present investigation was to determine the normal limits during the latter half of uncomplicated pregnancies, circadian and short‐time variations, and to evaluate the prognostic value of progesterone determinations in plasma in high risk pregnancies.