Egg-Freezing: What's the Success Rate?

The fertility expert, Lord Robert Winston, appeared on BBC Radio 4's Today programme to discuss the campaign to relax the current ten-year limit on freezing eggs.

Lord Winston, who is professor of fertility studies at Imperial College London, warned that it was "a very unsuccessful technology" and said: "The number of eggs that actually result in a pregnancy after freezing is about 1%." He later clarified he was referring to live births.

But the body which regulates fertility treatment in the UK - the Human Fertilisation and Embryology Authority (HFEA) - puts the success rate at closer to one in five - a far better chance than the one in a hundred Lord Winston suggests.

So, why the different figures?

It's because the two are measuring the success rate based on different stages of fertility treatment.
An IVF cycle involving frozen eggs goes something like this:

• Eggs which were previously frozen and stored are thawed
• The ones that survive the thawing will be fertilised with sperm
• Eggs that are successfully fertilised start to develop into embryos
• Of the embryos that...