[Plasma and intrafollicular hormone profiles in the late preovulatory phase. I. Spontaneous cycles]

The hormone state of development in the late preovulatory phase is described in its relationship to the start of the LH surge which occurs 37-39 hours before ovulation. No precise relationship has been found between the oestradiol (E2) peak in the plasma and that which occurs before ovulation. All the same, the succession of hormone events that have been observed in 77 spontaneous cycles is the following: the level of E2 suddenly rises between 35 and 30 hours before the ovulatory discharge and this rise is immediately followed by a rise in the level of LH. Then the plasma concentration of 17-hydroxyprogesterone (17-OHP) increases 5 hours before the LH surge. In the preovulatory follicle 5 hours after the start of the LH surge, a drop in the level of E2 and a rise in the level of progesterone is noted. Concentrations of androgens only lessen in the last 12 hours before ovulation whereas the level of 17-OHP stays stable. We have thus been able to work out the sequence of plasma hormone phenomena that occur in determining whether a preovulatory gonadotrophic surge will occur. We have described the hormone levels in follicular fluid immediately before spontaneous ovulation. These findings will be able to serve as a reference to evaluate the quality of the late preovulatory phase in abnormal cycles or in cycles that have been induced.