Timing of nuclear maturation and cumulus dissociation in human oocytes stimulated with clomiphene citrate, human menopausal gonadotropin, and human chorionic gonadotropin.

The maturation of the preovulatory human follicle larger than 16 mm is described between 0 and 36 hours after human chorionic gonadotropin (hCG) administration. The nuclear evolution of the oocyte is timed: prophase at 14 hours, germinal vesicle breakdown at 15 hours, metaphase I at 20 hours; metaphase II is complete by 35 hours. The quantified expansion of the cumulus is related to nuclear evolution. Almost complete expansion may already be observed 18 hours before ovulation (20 hours after hCG). The specific action of clomiphene citrate, human menopausal gonadotropin, and hCG stimulation on the granulosa induces a more rapid luteinization than is found after other means of stimulation or in spontaneous cycles. Oocytes from follicles less than or equal to 16 mm on preovulatory ovaries often show a reaction to hCG that may be related to their subsequent quality.