Normal, age-related changes occur in the ovaries as women get older. A woman is born with approximately one million egg-containing follicles in her ovaries. When she reaches puberty that number drops to about 300,000, of those follicles only about 300 will actually be ovulated throughout her reproductive years. Most of the follicles are not actually ovulated, but are lost through a degenerative process called atresia.
As you have probably heard, a woman’s best chance of conceiving is during her 20s. A gradual decline in fertility begins when a woman reaches her 30s, particularly after age 35. A healthy, fertile 30-year-old woman has a 20% chance of getting pregnant each month. By the time a woman is 40 years old, her chance of conceiving is less than 5% per cycle. Most women are unable to have a successful pregnancy by the time they reach their mid-40s. These percentages apply to both natural conception and conception that occurs by using fertility treatment. The loss of fertility occurs due to a decline in both egg quality and quantity.