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Why Do I Have Less Eggs Than Follicles and Even Fewer Embryos?

blastocyst culture Why Do I Have Less Eggs Than Follicles?

Why Do I Have Less Eggs Than Follicles and Even Fewer Embryos?

It is important to understand that not every follicle seen on ultrasound scan during an IVF cycle will have an egg collected from it.  It is expected that approximately 60-80% of follicles will yield an egg. 

Occasionally there are may be fewer eggs collected at the egg collection than might be expected and in some situations, there can be no eggs.  Having no eggs collected is sometimes seen when there are a low number of follicles noted on the final scan before egg collection i.e. four or less. 

Once the eggs have been collected, not every egg will fertilise. It is expected that approximately 60-80% of eggs will fertilise. However, once an egg has been fertilised, it does not necessarily mean it will be suitable for transfer or freezing.  Some embryos will grow until Day 2 or 3 (cleavage) and look perfectly normal, but do not progress after this stage. 

To demonstrate this, from the eggs that do fertilise it is expected that approximately 1/3 of these will reach day 5/6 (called the Blastocyst stage). So if 9 eggs are fertilised, it would be realistic to expect that approximately 6 embryos would be progressing at the expected 6 – 8 cell stage on day 3.  However, only 2 of these embryos may progress to day 5/6 – click here for more information.

eggs embryos blasts attrition chart

Once the embryos have reached this stage it does not necessarily mean they will be suitable for transfer or freezing. It’s important to realise that these results are very individual. 

If you have further questions, please don’t hesitate to speak with your specialist or the scientific team. 

For more information, please contact us.