Michelle Emblenton, biochemist at inviTRA, talks to us in this video about the concept of ovarian reserve:
In order to understand better the concept of the ovarian reserve I want to start by having a look at where do the eggs come from, when are they developed inside a woman's body and how does it get depleted over time. At the moment of embryonic development, when the future woman is still just a fetus inside her mother's uterus, the development of all of the eggs that she has begins and this process will actually end before the woman is born.
As a result, at birth, a woman will have all of the eggs that she will ever have in her lifetime and it is not possible to increase the number of the eggs after this time. So we can think of the eggs within the ovaries as a great treasure that the woman is born with. Indeed, a 20 week old fetus may have 6 to 7 million eggs. At birth, the baby may have about 1 to 2 million oocytes in their ovaries. And at puberty this number has probably decreased to around 300,000 eggs. From the onset of puberty, one egg will be released each month at ovulation.
However, what most people don't realize is that although one egg is ovulated there is actually a much more complicated process involving many many oocytes. Most of us are fully aware about the need for millions of sperm to create an embryo and the idea that there is competition amongst all these millions of sperm and the very best one gets to the egg, but what most people don't realize is a similar but on a smaller scale process, many oocytes are recruited all of the time so that the best oocyte is the one that matures and gets ovulated.
Indeed, every month approximately 12 or perhaps even more eggs will be recruited into the the maturation process, which can take up to 3 months. Only one of these oocytes will be ovulated and the rest of them will deteriorate and never to be released, that will be the end of them. So we can understand why we are born with many more eggs than we will ovulate and, by this process, the number of eggs you have left will gradually decline over the years until your supply is exhausted. The ovarian reserve is basically the number of a woman has at any given time in her life.
A couple of facts that we do know about the ovarian reserve is that it can never increase, since you are born with all of the oocytes that you will ever have, the number will only decrease over the years and, indeed, ovarian reserve does decrease over the years. This is a natural process until the onset of the menopause. However, there are external factors that can affect your ovarian reserve. For example, if you have had an ovary removed this will radically affect your ovarian reserve, since the ovary is where the oocytes are located. External agents such as radiotherapy or chemotherapy may also damage the oocytes and lower your ovarian reserve. In addition, the selection of the oocytes to develop into eggs is not related to the control of ovulation by the female hormones. As a result, contraceptive pills (which stop the ovulation) do not stop the selection and development of the oocytes. So a hormonal contraceptive won't stop the oocytes being selected into the development procedure and therefore won't affect your ovarian reserve.
