Salivary progesterone excellently reflects free and total progesterone in plasma during pregnancy.

To see if saliva is a valid substitute for plasma in assay of progesterone even when concentrations of hormone and binding proteins are fluctuating, we determined the concentrations of total and free progesterone in plasma and salivary progesterone in specimens from 36 women volunteers during the course of pregnancy and six weeks postpartum, using a highly specific RIA for total progesterone after extraction and chromatographic purification of the steroid. The free fraction in plasma was determined via equilibrium dialysis, followed by the same RIA analysis for progesterone in the dialysate. Despite the dramatic increases in concentrations of total progesterone and binding proteins in plasma during pregnancy, we found highly significant correlations between total and free progesterone in plasma and salivary progesterone in the group as a whole as well as individuals (P less than 0.001 in almost all cases). The proportion of free progesterone in plasma and of salivary progesterone relative to total progesterone in plasma remained constant at approximately 1% and 0.5%, respectively, whereas during the postpartum period there was much more variance. Evidently salivary progesterone is a very good alternative to plasma as a sample for use in follow-up during pregnancy.