Decline of follicular oocyte maturation inhibitor coincident with maturation and achievement of fertilizability of oocytes recovered at midcycle of gonadotropin-treated women.

To examine whether a decline in follicular oocyte maturation inhibitor (OMI) is associated with attainment of oocyte maturation and fertilizability, OMI was measured in follicular fluid (FF) of 39 follicles of 20 normal women given human menopausal gonadotrophin and human chorionic gonadotrophin to induce follicular growth and maturation. Oocytes were aspirated per laparoscope, the fluid was saved, and the egg was observed, incubated, and inseminated with the husband's sperm. Concepti that developed to the 4- to 8-cell stage were transferred to the uterus and the women were followed for pregnancy. OMI activity in each FF was measured by using cultured cumulus-enclosed porcine oocytes (30-40 oocytes per FF sample). Estrogen, progesterone, oocytes (30-40 oocytes per FF sample). Estrogen, progesterone, and delta 4-androstenedione were measured in FF by radioimmunoassay. The FF of 13 preovulatory follicles yielding oocytes that were mature and fertilizable had significantly less OMI activity (mean +/- SEM) (0.58 +/- 0.10 unit/ml) compared to follicles yielding immature oocytes (2.8 +/- 0.56 units/ml; n = 9), atretic oocytes (5.5 +/- 2.5 units/ml; n = 7), or preovulatory oocytes with fractured zonae (1.9 +/- 0.63 units/ml; n = 7). The estrogen concentration (mean +/- SEM) of preovulatory follicles yielding mature fertilizable eggs or mature eggs with fractured zonae was greater (396 +/- 34 ng/ml; n = 20) compared to follicles yielding immature or atretic eggs (203 +/- 59 ng/ml; n = 9 and 97 +/- 47 ng/ml; n = 7, respectively; P less than 0.05). Progesterone concentration (mean +/- SEM; ng/ml) of FF was generally elevated in all preovulatory follicles (635 +/- 53) compared to immature or atretic follicles (230 +/- 64 and 76 +/- 17, respectively; P less than 0.05). It may be concluded that in normal follicle maturation there is a decline in OMI in the follicle containing an oocyte that becomes mature and fertilizable. There is also an increase in estrogen, progesterone, and follicle size. It is also possible to have an abnormal follicle maturation when there is an increase in size as well as FF, estrogen, and progesterone, but withut a decline in OMI--a situation which can lead to production of a nonfertilizable oocyte.