A woman has her peak number of eggs (oocytes) before she is born. All during a woman's life, the eggs are decreasing and tens of thousands of eggs are lost every year of a woman's life. This is one of the main reasons why a woman's fertility decreases as she gets older.
As the eggs are being lost, the ovaries become smaller. Using transvaginal ultrasound, the volume of each ovary can be calculated by measuring the length, width and depth.
Once you know the ovarian volume, ovarian reserve, ovarian volume, ovary size, decreased ovarian reserve, time to menopause, reproductive age you can calculate a woman's "reproductive age." Her reproductive age may be older or younger than her actual age.
For example, a 35 year old woman with very small ovaries may have the reproductive age of a 40 year old. Alternatively, a 40 year old with very large ovaries, may have the reproductive age of a 35 year old.
Medical studies have correlated ovarian size with a woman's ability to respond adequately to fertility medications and to IVF. Women with small ovaries tend to respond more poorly to fertility medications than women with larger ovaries.
A very recent study has also suggested that you can predict how many years it will be before a woman reaches menopause by her ovarian volume.