Relationship between Serum Inhibin A and B and Ovarian Follicle Development after a Daily Fixed Dose Administration of Recombinant Follicle-Stimulating Hormone1

The aim of this study was to investigate the relationship of serum inhibin A and inhibin B to ovarian follicular development in women undergoing pituitary down-regulation and ovarian stimulation with a fixed daily dose of recombinant human FSH in an in vitro fertilization program. Thirty-eight patients were treated randomly with either 100 or 200 IU/day recombinant human FSH (Puregon) for a period of 9-14 days. Serum FSH, inhibin A, inhibin B, 17beta-estradiol, and follicular size and number were determined before FSH treatment and every second day from days 4-6 throughout FSH treatment. Serum FSH increased in a dose-related manner to reach a maximum by days 4-6 and remained unchanged over the duration of treatment. Serum inhibin A and 17beta-estradiol also increased with increasing FSH dose and continued to rise throughout the FSH treatment period. By contrast, serum inhibin B was increased by days 4-6 at both doses of FSH to reach a maximum by days 7-8, remaining unchanged thereafter. Serum inhibin B and, to a lesser extent, inhibin A correlated significantly with the number of oocytes retrieved even when assessed early (days 4-6) in the treatment period (inhibin B vs. number of oocytes: r = 0.89; P < 0.001; inhibin A vs. number of oocytes: r = 0.61; P < 0.05). Serum inhibin A, inhibin B, and 17beta-estradiol were weakly correlated with the number of follicles less than 11 mm when assessed on a daily basis; stronger correlations were observed with the greater than 11-mm follicles during the late stages of treatment. It is concluded that serum inhibin B levels determined during the early stages (e.g. days 4-6) of fixed dose FSH treatment provide an early indicator of the number of recruited follicles that are destined to form mature oocytes. In this context, serum inhibin B may be of predictive value in monitoring ovarian hyperstimulation treatment for in vitro fertilization.