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.
The Human Egg
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 across. 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 into 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 (the primordial stage), and some which are very large and almost ready to release their egg (the Graafian stage). This is so one follicle is always ready at the same time every month when ovulation occurs.
One egg is released every month, but many others are wasted at the same time.
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 begin the maturation process every month... but only one becomes dominant. The dominant egg continues to grow in the ovary until it overtakes the rest and 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.
A woman begins her life with thousands of eggs in her ovaries. But after many waves of eggs recruited for development, only to be lost during each menstrual cycle, they quickly deplete and eventually run out completely resulting in menopause.
IVF utilises the eggs which would have otherwise been lost that month.
To create embryos outside the body, eggs need to be collected from the ovaries so they can be fertilised in the laboratory.
Hormonal stimulation is used to take control over the development of egg-containing follicles in the ovaries. Rather than having one dominant follicle, the smaller follicles are allowed to grow simultaneously alongside it - rescuing the eggs which would normally be lost every month.
Ready to Learn More About Eggs?
Learn about how eggs are grown and collected for IVF, how eggs are handled in the laboratory and what to expect during an IVF cycle. Plus read about all the factors which can affect the number and quality of eggs and what you can do to improve your chances of success.
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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...