The effect of a GnRH antagonist on follicle maturation in normal women

Ganirelix is a gonadotrophin-releasing hormone (GnRH) antagonist used for the prevention of premature LH surge during ovarian stimulation. What is the impact of ganirelix on follicle maturation in normal women?

Ten normally cycling women were investigated during two menstrual cycles, i.e. cycle 1 (control) and cycle 2 (ganirelix). During both cycles, daily blood samples were taken from day 2, while transvaginal ultrasound scans were performed on cycle days 8 and 10 and daily thereafter. During cycle 2, all women were given 0.25 mg/day subcutaneous injections of the GnRH antagonist ganirelix from day 2 until the day of the endogenous LH surge onset in cycle 1.

During treatment with ganirelix, serum FSH and oestradiol concentrations remained stable, while those of LH decreased significantly on days 3, 4, 7 and 9 (P < 0.05) compared with controls. Nevertheless, there was no significant within-cycle variation in LH concentrations. From day 10 onwards, no follicle maturation was observed in cycle 2, in contrast to cycle 1. Ovulation occurred in 9 of 10 women in cycle 1. In cycle 2, ovulation was delayed by at least 1 week in eight women. Follicle growth and ovulation occurred in only one woman while on ganirelix treatment.

This study demonstrates for the first time that in normal women dominant follicle selection failed during treatment with ganirelix. As there was a similar gonadotrophin profile in the two cycles, it is suggested that ganirelix interferes with the process of follicle selection by acting in the ovary.