In the latest of our lunch-bite webinar series, Marta Wolska, Operations Director at London Egg Bank, talks to Dr Shailaja Nair, Clinical Director and Elena Linara-Demakakou, Lab Manager and Quality Lead at London Egg Bank about the differences in approach and outcomes when using fresh and frozen donor eggs. Though London Egg Bank provides IVF treatment with both, here we hone in on why frozen eggs, in particular, are now a popular choice
What is egg freezing and how does it work?
After egg retrieval, the first thing we look at is the quality of the eggs. If the eggs are mature enough and of a high enough quality, then we freeze them using our vitrification system. Vitrification preserves them in a glass-like state, and, once in this state, they can be stored at very low temperatures for years without losing quality, until the patient is ready to start treatment.
To be able to do this well, the clinic needs to have an excellent vitrification system and experienced staff who are skilled in dealing with the cycle of egg freezing and thawing.
At London Egg Bank we have frozen more than 30,000 eggs, and we have also thawed more than 10,000 eggs, and are always looking to improve our processes and monitor our results.
Due to our expertise and experience, we’re delighted to report that our eggs now have a 92% survival rate. The fertilisation of these frozen eggs is equally high and compares with a fresh egg rate – we're seeing 70 to 80% fertilisation, sometimes more.
And most importantly, the number of embryos that we can create from these frozen eggs is above 50% in most cases. We are also pleased to report that over 85% of our patients have extra embryos frozen for subsequent treatment.
Vitrification has transformed the way we offer treatment to patients, and as such, frozen eggs are now a very popular choice.
How do you assess the eggs for suitability?
Only eggs that are deemed mature and with a good chance of being usable at a later date are frozen. We look for the egg to have a good internal cytoplasm and a robust-looking polar body, which is a structure that tells us that the egg is mature.
If the egg is mature, it means that it's at the right stage to be either frozen or inseminated with sperm to, hopefully, fertilise, but if it hasn't reached that stage it's deemed immature. We don’t freeze immature or poor-quality eggs; only eggs that are of a good quality, are mature and are ready to be fertilised will undergo vitrification. Furthermore, having a good vitrification system means that you do not damage the egg (changing its chromosomal arrangements or DNA, for example).
At London Egg Bank, the egg survival rate isn’t our only focus. We have analysed live births from fresh and frozen eggs and have seen no difference. We've also looked at congenital abnormalities that were self-reported by the patient. While we can’t know of abnormalities that patients didn't report, we’ve looked at preterm births and any other implications that they might have had, and we couldn't see a difference when we compared fresh to frozen egg outcomes in our data.
Since we were established in 2013, London Egg Bank has consistently delivered the UK's highest recorded egg survival rates after freezing. We’re delighted to see that our donor eggs have a 92% egg thaw survival rate. The fertilisation of these frozen eggs is equally high and compares with a fresh egg rate, and we're seeing 70 to 80% fertilisation rates, sometimes more. And most importantly the number of embryos that we can create from these frozen eggs is above 50% in most cases.
How does using frozen eggs improve patient care?
Vitrification is a relatively new process that has revolutionised the way that we manage and deal with egg donation.
While fresh donor eggs are still popular, there are several drawbacks. For example, recipients who want to undergo a fresh embryo transfer need to be available at the same time as the egg donor. They and the donor are both asked to take the contraceptive pill to regulate and synchronise their cycles. The recipient also has to take an injection creating an artificial menopause, so that their natural cycle doesn't interfere with the process.
Fresh egg donation can also be unpredictable, as one can also never be certain about the donor’s response to stimulation. In about 10% of cases, the donor may not respond as well as we had hoped for, meaning that both the donor's and recipient's cycles has had to be abandoned.
Similarly, during egg collection, there have been instances where fewer eggs were retrieved than expected. This sometimes led to cycles being delayed, canceled, or yielding suboptimal results – primarily because both the donor and recipient had to undergo treatment simultaneously.
Now that we can use frozen eggs with the same confidence we used to have with fresh eggs, we have become used to a degree of convenience. Recipients can start treatment whenever they want. The donor has already finished her part of the treatment and the collected eggs are ready to be used at any time.
This has been a significant clinical advancement, revolutionizing the way we approach egg donation, with outstanding results – we have a 50% clinical pregnancy rate per embryo transfer, and half of our recipients conceive after a single embryo transfer. Additionally, over 85% have more than one embryo from just six eggs. This is truly a game-changer.
Does the timing of egg freezing make a difference to the outcome?
The time that the eggs were frozen doesn't make any difference to the outcome, due to our round-the-clock monitoring. All of our tanks, which store the frozen eggs in liquid nitrogen, are monitored and maintained 24/7. And we know the exact temperature and stability of the tank at any given time, to ensure that all eggs are kept in optimum conditions. As such, you can confidently use eggs that were frozen two years ago or two days ago!
When it comes to egg freezing for fertility preservation, rather than egg donation, the HFEA (the UK fertility regulator) is looking to extend egg storage limits from 10 to 55 years. Without vitrification, this length of storage would simply not be possible, and the data is available to back up the confidence of this decision.
Does using frozen eggs affect the quality of frozen embryos?
No, the quality is not affected in any way – and we have the patient data to prove this.
We're hitting over 50% success in the last year for frozen embryo transfers with frozen eggs. Having this level of confidence means that, in 99% of our cycles, we only put one embryo back to reduce the risks of multiple pregnancies.
Do you have experience with high sperm DNA fragmentation being an issue when using frozen donor eggs versus fresh ones?
We don’t see a significant difference between fresh and frozen eggs, but we look at every patient individually and we try to tailor the treatment to them. For example, if we have a patient with high DNA fragmentation, there are often ways that we can work around it, either with how we prepare the sperm or with the way that we're injecting the sperm into the egg, ensuring that we have lower DNA fragmentation and a lower percentage of oxidative stress.
Does transporting eggs affect success rates?
Most of our donors are recruited in London or Cardiff and eggs are then shipped to the right location when needed for treatment. Transporting eggs doesn’t affect their viability because we’re experienced with both national and international transport, with very robust protocols.
It's important to note that when we do transport eggs we monitor them very closely, so that we know the complete timeline of their journey – how they’ve travelled, whether there was any fluctuations in temperatures, and so on. This means that there should be no difference in clinical outcomes.