Aging Egg Supply
A female baby is born with all the eggs her ovaries will ever contain. As a woman ages past her mid-30s, her eggs gradually degrade, making it less likely that she will conceive naturally.
In American women in their 20s to mid-30s, over 35 out of 100 give birth for each Assisted Reproductive Technology (ART) cycle using their own eggs. As women age, the live ART birth rate gradually drops to about 20 out of 100 for each IVF cycle by age 39.
In women over age 43 that birth rate drops to about 5 or less out of 100 for each IVF cycle. Many women over age 40 choose to use donor eggs, which greatly improves their chances of giving birth to a healthy child.
While there is no definitive test of ovarian reserve, a woman's follicle-stimulating hormone (FSH) level can be measured to evaluate how well her ovaries are working. A high FSH level is a sign that the body is trying to stimulate the ovaries to make more egg follicles, but the ovaries are not responding and conception is unlikely.
A woman's FSH level can be tested using a blood sample.