Measurement of progesterone in saliva: assessment of the normal fertile range using spontaneous conception cycles.

The concentration of progesterone in saliva can be used as an alternative to the measurement of the hormone in plasma because the steroid profiles are qualitatively, although not quantitatively, similar. Reference values for concentrations of the hormone during the luteal phase have been established using data derived from selected, apparently normal women, some of whom conceived in the study cycle. Six to eight days after the LH surge salivary progesterone values of 300-800 pmol/l can be regarded as 'normal' and can therefore be used as a reference for the clinical assessment of infertile women. Moreover, since there is a significant within-subject, between-cycle correlation (P less than 0.001) in salivary progesterone index values, the clinical information derived from one cycle is likely to be representative for that individual.