The Life Cycle of a Woman’s Eggs

To understand the role of time in women’s reproductive life, it is worth discussing the life cycle of a woman’s eggs. Here, we share an overview of the current understanding of women’s eggs.

Women are born with all the eggs they will ever have. As a woman ages, these immature eggs are recruited for ovulation by the woman’s body during the menstrual cycle. At birth, a woman has over a million immature eggs, by puberty around 300,000, and at menopause, around 11,000.1 Just 300 eggs will ovulate during a woman’s lifetime.

Between the ages of 33 to 42 and at an average age of 38, the loss of immature eggs accelerates. This acceleration marks the onset of the decline in a woman’s fertility, which eventually leads to menopause. Aging not only limits the number of eggs that can be recruited, but it also decreases the quality of those eggs. There are several things that can accelerate this decline in quantity and quality—such as smoking, exposure to certain medications, etc.—but nothing has currently been proven to slow down the egg-aging process.

1 Faddy, M.J., Molecular and Cellular Endocrinology 163 (2000).