Inhibin-B

Definition - What does Inhibin-B mean?

Inhibin-B is a hormone produced in both females and males by the ovaries and testes respectively. In females, the small follicular cells of the ovaries produce inhibin-B. As the name indicates, inhibin-B functions to inhibit the production of follicle-stimulating hormone (FSH) by the pituitary, and thereby inhibits the growth of follicles. The levels of this hormone fluctuate during the menstrual cycle and are measured on day 3 of the cycle to determine the ovarian reserve, including the egg quality and quantity. Ovarian reserve implies the pool of follicles remaining in the ovaries at any phase of the menstrual cycle.

FertilitySmarts explains Inhibin-B

During the follicular phase of the menstrual cycle, the ovarian follicles develop under the influence of FSH, with one of the follicles becoming dominant to release an egg. Inhibin-B inhibits these follicles from growing. The blood levels of inhibin-B are highest in the early to the mid-follicular phase when the follicle growth is at its peak (day 3 of the menstrual cycle), with a second peak observed at the time of ovulation. These levels of inhibin-B reflect the number of follicles in the ovaries. As a woman ages, the blood levels of inhibin-B fall because of the decline in the size of the follicle pool that occurs with aging. Low levels of inhibin-B at that time, thus, reflect a poor ovarian reserve, poor egg quality, and a compromised ability of a woman to ovulate and conceive.

As the ovarian reserve diminishes, it becomes quite difficult for the hormones used during IVF to stimulate follicle development. This, in turn, lowers the chances of success with IVF.

Conversely, higher levels of inhibin-B reflect a good ovarian reserve or the presence of a good amount of follicles in the ovaries.

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