Studies on the pattern of circulating steroids in the normal menstrual cycle. 2. Levels of 20alpha-dihydroprogesterone, 17-hydroxy-progesterone and 17-hydroxypregnenolone and the assessment of their value for ovulation prediction.

Plasma levels of 20alpha-dihydroprogesterone, 17-hydroxyprogesterone and 17-hydroxypregnenolone were assayed daily in 15 normally menstruating women during a complete menstrual cycle. In order to ascertain the normalcy of the cycles studied, LH, progesterone and oestradiol were also determined daily. The pattern of 20alpha-dihydroprogesterone was very similar to that of progesterone. The levels found during the proliferative phase (around 240 pg/ml) increased significantly on the day of the LH-surge and reached values of approximately 3.7 ng/ml at the peak period of luteal activity. The plasma levels of 17-hydroxyprogesterone in the proliferative phase were around 380 pg/ml. The first significant increase occurred one day before the LH-surge and was followed by a sharp peak (approximately 1.5 ng/ml) which coincided with the LH peak. A significant decrease occurred after this peak, which reached a nadir two days after the LH-surge. This was followed by a second rise with a rather broad peak (about 1.8 ng/ml) around the 5th to 7th days after the LH-surge. The levels of 17-hydroxypregnenolone did not show any cyclic variation: from all figures a geometric mean value of 1.62 ng/ml was calulated with tolerance limits at 0.241 and 10.8 ng/ml. Individual day-to-day changes in steroid levels were assessed with regard to their potential for the early identification of the day of the LH-surge. A 17-hydroxyprogesterone value of 1.0 ng/ml, or more, was seen for the first time in the cycle on the day of the LH peak in 13 cycles and a progesterone + 17-hydroxyprogesterone level of at least 1.8 ng/ml in 14 of the 15 cycles studies. These data seem to warrant a study of the predictive value of progesterone and 17-hydroxyprogesterone assays in a much larger population.