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Why does the ovarian reserve of eggs decrease as women age?

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Diagram showing the female reproductive system with labeled ovaries, fallopian tubes, uterus, and vagina, alongside hormone pathways and the process from ovulation to fertilization and early embryo development. — infertility Major structures and hormones involved in the initiation of pregnancy. Also seen, at right, is the development of an egg cell (ovum) from follicle to embryo.

The decline in a woman's ovarian reserve of eggs is a natural consequence of aging. The natural life span of the ovaries is approximately 35 years, and the reduction in the number of follicles—which contain the eggs—is a normal physiological process that accelerates as a woman approaches menopause.12

During a woman's reproductive years, follicles mature and release ova periodically. However, as age increases, the ovaries contain fewer functional follicles, eventually consisting mostly of shrunken or atretic tissue. This depletion of the ovarian reserve is a primary factor in the age-related decline of female fertility, which typically begins to decrease in a woman's mid-30s. While this process is a standard biological progression, it ultimately leads to the permanent cessation of reproductive function.21