Characteristics of ovarian follicles in spontaneous and stimulated cycles in which there was an endogenous luteinizing hormone surge.

The growth of ovarian follicles was assessed with the use of ultrasound in spontaneous cycles and in cycles stimulated with clomiphene citrate (CC) alone, CC plus pulsatile human menopausal gonadotropin, and CC plus pulsatile follicle-stimulating hormone (FSH). At the time of the onset of the luteinizing hormone surge (LH), the size of the leading follicle did not differ significantly between the spontaneous and the stimulated cycles, although it was larger in the CC/FSH cycles. During the two days before the LH surge onset, the growth rate was faster in the stimulated than the spontaneous cycles. It is suggested that despite the provocation of extremely high plasma-estradiol levels and multiple follicular development, the leading follicle in stimulated cycles ovulated at a size equal to or greater than that in spontaneous cycles. The reason for the higher follicle size in the CC/FSH cycles is, as yet, unclear.