As a woman ages her egg supply diminishes with respect to both the quantity and the quality of the remaining eggs. A female is born with all of the eggs that she will have to ovulate with throughout her lifetime. Therefore, as a woman ages the eggs are depleted and not replaced. Additionally, as a woman ages so does her eggs. With a lower number of eggs, and lower quality eggs the per cycle pregnancy rate decreases as a woman ages. In addition to a decreased chance for pregnancy there are also increased risks for miscarriage, and babies with an abnormal set of chromosomes such as trisomy 21 (Down syndrome).