The value of a single serum progesterone measurement in the midluteal phase as a criterion of a potentially fertile cycle ("ovulation") derived form treated and untreated conception cycles.

A single midluteal serum progesterone concentration was obtained in 212 untreated cycles in 113 infertile patients, including 138 cycles in 72 patients in whom tubal, seminal, and cervical causes of infertility had been excluded. There were 16 conception cycles in the latter group. In an extended study a total of 21 untreated singleton conception cycles have been observed with a mean progesterone value of 40.7 nmol/l (12.8 ng/ml), 95% confidence limits of 28 to 53 nmol/l (8.8 to 16.7 ng/ml), and a range of 27 to 53 nmol/l (8.5 to 16.7 ng/ml), which extended significantly above as well as below the conception range, indicating that there is an optimal range for fertility with both an upper and a lower limit. The lower limit is of greater practical importance; and, partly to allow for assay variation, we suggest it should be taken as 30 nmol/l (9.4 ng/ml). It provided a clinically reliable criterion of potential fertility ("ovulation") in related studies. Our findings in treated conception cycles suggest that a higher value may be needed after treatment with clomiphene or gonadotropins because of the contribution from other stimulated follicles.