This chart provides a quick look at the natural chances of pregnancy by age.
As you may know, women are born with all the eggs they'll ever have. At birth, the number of eggs in a woman is typically around 1 million. By puberty, she usually has half that. Each month, women lose up to 1,000 eggs monthly. Out of them, only 1 egg cell is matured and ovulated on a monthly basis.
Egg quality diminishes with age as well. This is the reason why, in addition to having a decreased ovarian reserve, a woman is more likely to have genetically abnormal eggs as she gets older.