Follicular fluid levels of inhibin A, inhibin B, and activin A levels reflect changes in follicle size but are not independent markers of the oocyte's ability to fertilize

Objective: To investigate the biochemical relationship between follicular/oocyte maturity and follicular inhibins and activin levels. Design: Prospective study. Setting: Research laboratory in university hospital. Patient(s): Thirty-five women undertook IVF/ICSI program. Intervention(s): Individual follicular fluid aspirations, oocyte isolation, follicular fluid storage. Main Outcome Measure(s): Inhibin A, inhibin B, and activin A concentrations, oocyte retrieval, and fertility outcome. Result(s): Inhibin A, inhibin B, and activin A concentrations varied from 7.9 to 436 ng/mL, 9.7 to 786 ng/mL, and 1.7 to 267.9 ng/mL, respectively. There was no change of inhibin A concentrations, whereas inhibin B and activin A concentrations dropped dramatically as the follicles enlarged. Total follicular content of inhibin A and activin A increased, and inhibin B remained constant. Both inhibin A and inhibin B levels were significantly higher in those follicles from which an oocyte could be recovered, but they did not differ with respect to subsequent oocyte fertilization. Conclusion(s): Inhibin A is actively produced throughout follicular growth to retain a set concentration. In contrast, inhibin B appears not to be actively produced, and the concentration drops as follicles enlarge. Activin A concentrations also decrease, but there is some extra synthesis. Higher levels of inhibin A and B are associated with oocyte presence but not with fertilization rates.