AMH (Anti-Mullerian Hormone) is secreted from follicles in the early stages of maturation (primary follicles to pre-follicles). The AMH level can be measured by a blood test, and if the value is high, it is estimated that there is a large stock of follicles. Conversely, if the value is low, it is possible that menopause is near. Menopause usually occurs around the age of 50, but premature menopause occurs in 0.1% of women in their 20s and 1% of women in their 30s. An AMH test can help you find out if you have a possibility of premature menopause.
However, a low AMH level does not mean that you cannot get pregnant, and a high AMH level does not mean that you are likely to get pregnant. It is not only the number of follicles that matters, but also the quality of the oocytes. Still, AMH is useful information.
For more information about AMH, please see this page.