Female fertility is closely associated with the activity of the ovaries, or more specifically with the active ovarian follicles found in the ovaries. Ovarian follicles and the egg cells they contain are formed in the body before a woman is even born, and many have already decayed by birth. This process continues after birth - but at this point there are hundreds of thousands of ovarian follicles. Of these, a few hundred are activated over the course of a woman’s life, but only approx. 400 ripen to ovulation during the fertile period.
At menopause, there are still several thousand ovarian follicles in the body, but they are no longer active. Most women continue to have ovarian function beyond the age of 40, meaning that they ovulate regularly, and ultrasound imaging shows a normal level of active ovarian follicles. However, in some women, ovarian activity is reduced from a much earlier point. There are many causes for this, and in many cases the causes remain unknown (e.g. genetic causes, autoimmune diseases, smoking). The ovarian reserve can be determined using ultrasound and by measuring the levels of follicle stimulating hormone (FSH) and Anti-mullerian hormone (AMH). The latter hormone in particular, which is formed in the small active ovarian follicles, provides information on ovarian activity.