In spontaneous cycles both LH and FSH are secreted in a surge at midcycle. In in vitro fertilization (IVF) cycles, hCG administration results in elevation of LH-like activity only. The objective of this study was to compare the effectiveness of a single midcycle dose of GnRH agonist with hCG on follicular maturation. Eighteen IVF cycles in 14 women were randomized to receive either 0.5 mg leuprolide acetate or 5000 IU hCG at midcycle. Both groups underwent identical ovarian stimulation and cycle monitoring. On the day of GnRH agonist or hCG administration, estradiol concentrations and the number of follicles 1.5 cm or larger were the same in both groups. Mean serum LH and FSH levels were elevated for 34 h after GnRH agonist administration. In contrast, mean serum hCG levels were elevated for approximately 6 days after the administration of hCG, and serum FSH levels did not change. Mean luteal phase serum estradiol concentrations were lower in the GnRH agonist group than in the hCG group (P less than 0.02). No differences were observed in mean serum progesterone or PRL during the luteal phase or in the length of the luteal phase in the two groups. The mean number of oocytes retrieved and embryo number and quality did not differ between the two groups. Three of nine GnRH agonist cycles and none of nine hCG cycles resulted in clinical pregnancy (P = 0.1). The results of this study indicate that GnRH agonist is able to simulate a midcycle surge of gonadotropins, leading to follicular maturation and pregnancy. Further work is needed to determine whether there is any clinical advantage of GnRH agonist over hCG administration with regard to pregnancy rates.
