Final answer:
At birth, female ovaries contain all the eggs they will ever produce, but they only mature and are released during ovulation starting from puberty until menopause. Each month during the reproductive years, typically one egg completes development and is released, which could potentially be fertilized.
Step-by-step explanation:
At birth, all the eggs a female will ovulate during her lifetime are already present in the ovaries, but they are immature and do not begin to mature until the female reaches puberty. At puberty, the process of oogenesis resumes, and eggs start maturing on a monthly basis during each menstrual cycle. Each month, typically one egg matures and is released in a process called ovulation. This continues until menopause, by which time the supply of viable eggs has usually been depleted.
A baby girl is born with between 1-2 million immature eggs, which decline in number to about 40,000 by the time she reaches puberty due to a natural process where the eggs die off. The eggs that are released each month from puberty until menopause are the ones that have completed development. Ovulation allows for the possibility of fertilization if the egg encounters sperm within the fallopian tubes.