Measurement of Serum LH, FSH, Progesterone, 17-Hydroxyprogesterone and Estradiol-17β Levels at 4-Hour Intervals During the Periovulatory Phase of the Menstrual Cycle*

Serum LH, FSH, 17-hydroxyprogesterone, estradiol-17β and progesterone were measured in 4 women every 4 hr during the midcycle LH surge to ascertain more exactly the relationship between 17-hydroxyprogesterone and estradiol-17β and LH. All women ovulated following their LH surges as indicated by a rise in serum progesterone. All LH peaks were preceeded by a surge of estradiol-17β as shown previously in normal menstrual cycles. 17-Hydroxyprogesterone rose after the onset of both the estradiol and LH surges. It was concluded that the dramatic rise in serum 17-hydroxyprogesterone at midcycle is the result of increasing levels of LH and is one of the earliest luteinizing effects of LH. Serum estradiol levels had started to decline prior to the LH surge in two subjects but not in another. A decrease in circulatory estradiol may not, therefore, be the mechanism for the midcycle release of LH.