Embryo grading

To ensure that you have a good chance of getting pregnant it is important that the best quality embryos are selected for transfer, especially when only 1 embryo is transferred at a time.

To ensure success if the first transfer fails, it is also important that the embryos most likely to survive freezing and thawing are selected for storage.

Embryologists therefore play an important part in the success of your treatment – they decide which embryos are transferred and which are frozen and stored.

When are embryos transferred?

Embryos can be transferred back to your womb at different times of their development. This may help to decide which embryo has the best chance of carrying on developing to establish a pregnancy.

• Sometimes embryos can be selected on day 2 or 3 of their development (known as cleavage stage embryos).
• Others may be left in the laboratory until they reach what is called the blastocyst stage, when they are approximately 5 days old.

What happens to the remaining embryos?

After an embryo transfer, an embryologist carefully assesses the quality of any remaining embryos to select which embryos are suitable for freezing and storage.

Good quality embryos can be frozen and stored to be used in follow-on treatment if the first transfer using the fresh embryo is unsuccessful.

Higher quality embryos have a better chance of surviving the freezing and thawing process.

What qualifications and experience does an embryologist have?

Clinical Embryologists are state-registered scientists who have:

• at least a degree (some have MScs or doctorates) in one of the life sciences (biology, genetics, etc)

and have either:

• completed the Association of Clinical Embryologists Certificate or
• at least six years experience to gain registration with the Health Professional Council.

How do embryologists make their decisions?

Embryologists use their training and experience to assess embryos and select those most likely to implant in the womb and continue to develop.

They do this by applying a system of grading, using criteria for early stage embryos such as:

• the number of cells present
• how fast the cells are dividing
• whether the division is even
• whether there are any fragments of cells present – this means that some cells have degenerated.

Different grading schemes are used for embryos when they reach the blastocyst stage (around day 5 of their development).

After the grading system has been applied to the embryos, any suitable ones are selected for transfer and storage.

Grading systems vary slightly, depending on your clinic, but they all produce similar results.