Silvia Azaña, embryologist at inviTRA, explains in this video whether egg quantity and quality are the same thing:
One point that is very important to clarify is that egg quantity and quality are not the same. The ovarian reserve of a woman, that is to say, the number of eggs, is already established at the moment of her birth. Approximately, girls are born with a number between 1 and 2 million of immature eggs. However, when they reach puberty, the ovarian reserve has already decreased to about 500,000 uses.
From this point forward, a woman will continue to release one mature egg during each menstrual cycle. However, other eggs will undergo a process of atresia and will be lost. With all this, the ovarian reserve of a woman decreases as time goes by, until it is completely depleted by the time she reaches menopause.
However, not only does the number of eggs decrease with age, but their overall quality also tends to decline. As you get older, it's more likely that your eggs will develop chromosomeal issues. This means that embryos may develop with chromosomeal issues or abnormalities, potentially leading to miscarriage or even the birth of a child with a health condition. Therefore, even if a 40-year-old woman has a good number of antral follicles seen on ultrasound, meaning she has a good ovarian reserve, it does not mean that these eggs are of good quality. The age of the woman is crucial for ensuring the eggs are of good quality. Starting at approximately 35 years of age, the eggs tend to be of lower quality, and their quantity decreases as well.
