Follicle-stimulating hormone (FSH) is produced by the pituitary gland situated at the base of the brain. It is released from this gland into the bloodstream and plays an essential role with regards to the ovaries. Its purpose is to stimulate follicle growth and selection and it also plays a role in maturing the egg which will later be released during ovulation.
In cases of ovarian insufficiency, the pituitary gland attempts to compensate for this by increasing FSH secretion. This happens in a physiological manner during the menopause and, as a result, women going through this stage have FSH levels which are far above those in women of childbearing age.

If abnormally high levels of FSH (>10 lU/L) are detected at a young age, this can be a suggestion of low ovarian reserve which reduces the possibility of getting pregnant naturally. […]