Women are born with hundreds of thousands of eggs in their ovaries which stay there until puberty. When a woman has her first period the menstrual cycle begins and the store of eggs starts to reduce.
What are eggs?
Eggs are also referred to as oocytes. They are the female reproductive cells - the equivalent of a sperm cell in men.
Although eggs are the largest cell in the body, they are still extremely small... around 0.2mm. They grow in the ovaries in large fluid-filled sacs called follicles which provide protection and support. It takes many months for a single egg to grow to full maturity before it is ready to be released, so at any one point in time the ovary has several follicles at different stages - some at the smallest stage, and some which are very large and almost ready to release their egg. This is so one follicle is always ready at the same time every month when ovulation occurs.
If you start your life with thousands of eggs, how do they all run out by menopause?
Every month one egg is released from the ovaries. If that egg is not fertilised, the lining of the womb is shed and the egg simply degenerates so it is lost. Although only one egg is released from the ovary, many eggs are selected from the pool every month... all hoping to become the chosen one. At the start of each cycle all of the selected eggs start to develop but only one becomes dominant. The dominant egg continues to grow in the ovary until it is finally released at ovulation in hopes of being fertilised. All the other eggs which started growing at the same time were not strong enough to become the dominant egg and they are now lost from the pool. This means that every month each ovary loses several eggs, and unfortunately most of them are wasted.
After months and months of waves of eggs being recruited for development, only to be lost during each menstrual cycle, they eventually run out completely and this is menopause.
How are eggs used for IVF?
To create embryos outside the body, eggs need to be collected from the ovaries so they can be fertilised in a laboratory. This is done using hormonal stimulation which rescues the eggs that would have otherwise been lost during a normal menstrual cycle.
Ready to Learn More About Eggs?
One of the biggest factors determining the success of IVF treatment is the quality of the eggs (oocytes). Although men can continue producing sperm for their whole lives, women are born with a set number of eggs which...