Frozen embryos are just as likely to result in a successful pregnancy as fresh ones, a landmark new study suggests.
Researchers discovered the technique, considered ‘controversial’, was slightly more effective in terms of live birth rates.
The new results, set to be published in The New England Journal of Medicine, were drawn from a trial of nearly 800 infertile women.
Frozen embryos resulted in pregnancies for 36 per cent of women – compared to 35 per cent in the fresh group, the ‘reassuring’ study found.
They were also more likely to result in children being born alive, with 34 per cent in the frozen group compared to 32 per cent in the fresh.
The ‘important’ findings dispute Government figures from 2010 that revealed frozen embryos were 10 per cent less likely to result in pregnancy.
Researchers discovered the frozen embryo technique, considered ‘controversial’, was slightly more effective in terms of live birth rates
An array of evidence has emerged in recent years to show that those embryos which have been thawed are ‘arguably better’.
The latest findings, led by Australian and Vietnamese researchers, offer more hope of making it the main option for IVF treatment in future.
Professor Ben Mol, co-author, based at the University of Adelaide, described the study as ‘important news for infertile women worldwide’.
He said: ‘Our key finding is that freezing embryos for IVF is not harming a couple’s chances of having a baby.
‘After the first fresh embryo transfer, it will be possible to freeze the remaining embryos and transfer them one by one, which is safe and effective.’
However, skeptics have repeatedly warned that if the method was more widely used it would lead to less pregnancies.
Aileen Feeney, chief executive of Fertility Network UK, welcomed the findings.
She said: ‘One of the big questions for couples experiencing IVF is whether there is any difference in the chance of having a healthy baby if they use fresh embryos or ones that have been previously frozen.
FROZEN EMBRYOS: THE FACTS
Often in IVF, women have good quality embryos leftover which they can’t use.
Instead of discarding them, they have the option to freeze them to use in the future.
Not all embryos are suitable for freezing so only good quality embryos will be chosen to freeze.
Embryos can be frozen at different stages of their development – when they’re just a single cell, at the two to eight cell stage or later in their development – the blastocyst stage.
The embryos will be put in a special substance, which replaces water in their cells.
This will protect the embryos from damage caused by ice crystals forming.
They’ll then be frozen, either by cooling them slowly or fast freezing (vitrification) and stored in tanks of liquid nitrogen until you’re ready to use them.
‘This study, although small, offers a measure of reassurance that there appears to be no significant difference in success rates between fresh and frozen embryos when using this particular freezing method.’
Professor Luciano Nardo, clinical director at Reproductive Health Group based in Daresbury, Cheshire, said: ‘Techniques to freeze embryos have been evolving at such a rate they are now lightyears ahead of where we were just a decade ago.
‘As techniques have evolved, the success rate has also risen, and we’re now at a stage where frozen embryo transfer cycles are as good, if not better, than fresh transfer cycles.
‘This research will no doubt reassure women worldwide about the effectiveness of using frozen embryos. It will also serve as an important reminder for couples suffering from infertility that there is hope.’
The majority of IVF clinics in the UK rely on the fresh embryo technique, when eggs are taken, fertilised soon after and then implanted.
Figures suggest just one in five cycles of IVF use the frozen technique – when ‘spare’ embryos from a previous attempt are kept frozen.
Clinics have moved towards the latter in recent years amid the recent studies which have proven freezing embryos is just as effective – but fears still exist.
Figures also suggest a fresh cycle is three times more expensive than a frozen one, suggesting price is also stopping some from making the transition.
Dr Lan Vuong, lead author, based at My Duc Hospital, Ho Chi Minh City, said: ‘Frozen embryo techniques are growing in popularity in fertility clinics worldwide.
‘This is one of the reasons why our research is important for fertility clinicians and researchers, and of course couples who are hoping to have a child.’
In the UK, women can store their embryos for 10 years by law. Those with certain circumstances can keep them for 55 years.
None of the women in the study suffered from polycystic ovarian syndrome – which is estimated to be responsible for almost a third of all infertility diagnoses.
One cycle of IVF was given to all. Success rates for the fertility treatment vary, with a steep decline for women over the age of 34.
The women were then given either a transfer of fresh embryos or those which had been thawed without the use of controversial IVF drugs.
Studies have repeatedly highlighted the dangers of the drugs used, with Swedish experts finding they can raise the risk of fatal blood clots in 2013.
The researchers warned the results of this latest trial on frozen embryos are specific to a common freezing method called Cryotech vitrification.
It is considered to be the ‘most effective, easiest and safest method’ of preserving oocytes and embryos of any developmental stage.
The findings may not apply to all the embryo freezing techniques currently being used, Dr Vuong also warned.
BUT THE GOVERNMENT INSISTS FROZEN EMBRYOS ARE LESS SUCCESSFUL
Data from the Human Fertilisation and Embryology Authority in 2010 found that frozen embryos were less likely to result in pregnancy.
There was a 23 per cent success rate for frozen and a 33 per cent chance for fresh embryos, the BBC reports.
But success rates for IVF using frozen embryos have been increasing year on year and are now much more comparable to rates using fresh embryos.
Having said that, births per embryo still tend to be fractionally higher for fresh embryos than for frozen, except for women over the age of 38.
This may be because the embryos transferred in the frozen cycle were created using eggs collected some time ago, when the woman was younger.