Reliability of a single serum progesterone determination as an indicator of ovulation.

Nine normal cycling subjects were monitored for mid-cycle LH surge and a subsequent rise in serum progesterone levels. Frequent samples were then taken for progesterone measurement during 8 h sessions in the early, mid and late luteal phases. These data showed: that progesterone secretion is pulsatile throughout the human luteal phase, with maximum frequency in the mid-luteal phase; that during the mid-luteal phase most subjects had progesterone levels both above and below currently accepted ovulatory thresholds; the use of a single measurement of progesterone in the mid-luteal phase is not always a reliable indicator of ovulation; a threshold greater than 20 nmol/l may yield an unacceptable number of false negative results.