Question: how and why do bad eggs cause problems and what can them problems be ?

Caroline Dalton answered on 19 Jun 2012:

Great question! The egg is the female reproductive cell that is fertilised by the male reproductive cell, the sperm, in order to make a baby. In some women these eggs are not very healthy and so even if they meet the sperm they might not grow into a baby, or the baby might have problems in its development.

For example, some eggs might not be able to be fertilised even if they meet a sperm as there is something wrong with the egg that means the sperm can’t bind and get into the egg. In other cases the sperm might be able to fertilise the egg but then the egg doesn’t divide properly and isn’t able to grow into a baby. This means that some people have difficulty in having a baby if they have lots of these eggs which aren’t very competent or which are “bad” as they don’t get fertilised properly or don’t grow properly into a baby.

In some other cases the sperm might fertilise the egg and it grows into a baby but that egg had one extra or one less chromosome and this can lead to problems for the baby. Downs syndrome for example is caused by having an extra chromosome 21.