Q: What does Inhibin B mean?

A: FSH is made by the pituitary gland in the brain and Inhibin B is made only by the follicular granulosa cells in the ovary. Both levels reflect on the potential of the ovary to grow follicles, which physicians refer to as 'ovarian reserve.' The FSH hormone stimulates the growth of ovarian follicles, and in response to this stimulation the ovaries increase production of a substance called Inhibin B. Inhibin B then tells the pituitary gland that the ovary has responded, and that an adequate number of follicles is present. In response, the pituitary gland stops producing FSH. A good ovarian response is indicated by a low FSH level and a high inhibin B level on cycle day 3. If the FSH level or estradiol level are high, or if the inhibin B value is low, that generally indicates that ovarian reserve and fertility are significantly diminished, specifically in women in the late 30s or early 40s. Diminished ovarian reserve means you are less likely to ovulate.