Follicular development and oocyte maturation in hypogonadotrophic women employing recombinant follicle-stimulating hormone: the role of oestradiol

Both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are required for follicle development and oestrogen production. Moreover, under normal conditions a close association between dominant follicle size and serum and intrafollicular oestradiol levels is observed. With the recent availability of human recombinant FSH (recFSH), it was possible for the first time to study effects of FSH alone, in the complete absence of endogenous or exogenous LH, on ovarian function. Recent studies applying recFSH in hypogonadotrophic women have shown convincingly that normal growth of follicles up to the preovulatory stage occurs despite extremely low oestradiol levels, in keeping with previous observations using exogenous gonadotrophins in women incapable of synthesizing oestradiol due to steroid enzyme abnormalities. Insufficient data are presently available in humans to conclude whether or not oocyte quality is compromised under these circumstances. It should, however, be realized that sufficient oestradiol levels are required for fertilization in vivo. Therefore LH, or human chorionic gonadotrophin (HCG), should be added to stimulation protocols in hypogonadotrophic individuals. These observations may also be relevant for monitoring of ovarian response during recFSH therapy, especially when combined with gonadotrophin-releasing hormone agonists for ovarian hyperstimulation for in-vitro fertilization.