More women are choosing to delay child bearing until after the age of 35 -- the very time when they are more likely to realize a marked decline in fertility potential. This decline in 'ovarian reserve' is a natural consequence of aging, but a clinical challenge to prospects for pregnancy.

Girls are born with a reserve of about 2 million eggs. By puberty, girls have about 300,000 eggs and the decline continues until menopause. From this reserve, a woman will ovulate only about 500 eggs during her reproductive years.

As women age, their ovaries produce declining levels of hormones. That not only undermines ovulation; it increases chances of miscarriage by injuring the chromosomal quality of eggs.

Besides using age to determine pregnancy chances, we can use hormonal testing to gain insight into egg quality. An elevation of Follicle Stimulating Hormone (FSH) or Estradiol levels bodes poorly for pregnancy chances. A normal value indicates that one can expect age-appropriate fertility chances.