What is meant by the biological clock or ovarian reserve?
A female fetus starts out with more than one million immature eggs and this number decreases steadily so that at the time of puberty, there are approximately 200,000 eggs remaining in the ovaries for future ovulation. Many eggs are recruited each month but in a natural cycle only one egg matures. Menopause refers to the time when all viable eggs have been used up and this generally occurs in the mid to late 40’s. The biological clock therefore refers to the time starting with puberty and ending with the menopause during which the number of eggs decreases steadily. As a woman approaches menopause, the ovaries become more resistant to stimulation producing fewer eggs than they did in the years before. For some women this ovarian resistance can start in the 30s and even occasionally in the teens and early 20’s. There are a number of ways of estimating ovarian reserve; the most common is to measure the FSH and the estradiol on the second or third day of the menstrual cycle. An FSH level ov
