Concentrations of AMH and inhibin-B in relation to follicular diameter in normal human small antral follicles.

Background: The aim of the present study was to determine the intrafollicular concentrations of anti-Müllerian hormone (AMH), inhibin-B and steroids in normal human small antral follicles and to relate them to follicular size.

Methods: A group of 103 women having one ovary removed for fertility preservation by cryopreservation prior to gonadotoxic treatment served as a source of a total of 272 human small antral follicles. Prior to cryopreservation of the ovarian cortex, fluid from small antral follicles were collected. On the basis of the follicular volume, the diameter was calculated and follicles with diameters from 3 to 12 mm were included.

Results: Concentrations of AMH decreased significantly (P < 0.0005) from 1124 +/- 158 ng/ml (mean +/- SEM) in follicles with a diameter of 3 mm to a concentration of 392 +/- 98 ng/ml in 9 mm follicles, followed by a reduction to below 100 ng/ml in 12 mm follicles. The concentrations of inhibin-B rose from 57 +/- 10 ng/ml (mean +/- SEM) in 3 mm follicles to 142 +/- 10 ng/ml in 12 mm follicles (P < 0.0005) with a peak concentration of almost 200 ng/ml in 9-10 mm follicles. Relating hormone concentrations with age showed that even follicles from girls younger than 10 years showed the same range of AMH concentrations as those from older girls or women.

Conclusions: The intrafollicular concentrations of AMH become progressively lower with increasing follicle diameters. In contrast, concentrations of inhibin-B increased with increasing follicle diameter with peak values at around 9 mm in diameter. This suggests that AMH and inhibin-B undertake important intrafollicular functions around the time of normal follicular selection in the mid-follicular phase of the menstrual cycle.