Fresh is best. It sounds logical and is promoted by some clinics as the ‘gold standard’. But it is a mantra that could be stood on its head in terms of the most effective use of IVF embryos to maximise the chance of an on-going pregnancy and health baby.
The traditional practice of IVF is to transfer the ‘best looking’ embryo into the uterus immediately after a stimulated cycle.
Following the development of techniques for freezing and thawing embryos, in the 1980s, if a couple has more embryos that appear to be developing normally in the lab, they can be frozen for later use. More recently, we have seen dramatic improvements in the techniques for freezing these so-called excess embryos. In 2006, Genea was the first clinic group in Australia to introduce a new freezing method called vitrification – or snap freezing – as standard practice.
We were confident that snap freezing would be an advantage. It involves bringing the temperature of embryo down to -196 degrees in about 60 seconds, rather than the previous slower method that took about two and half hours. Speeding up the process reduces the risk of ice crystals forming that could damage the embryo and more than 95 per cent of embryos survive the freezing and subsequent thawing process.
But we have been surprised at just how good our results from frozen embryos have been for our patients.
Remembering that the ‘best looking’ embryo would still usually be transferred fresh, logic would dictate that the success rate from frozen embryo transfers would remain lower.
But what we have found at Genea, is that success from a frozen transfer is now almost on a par with fresh transfer. In fact, almost 50 per cent of frozen embryo transfers in Genea patients aged less than 38 will result in a pregnancy – compared to a success rate of less than 25 per cent just five years ago.
There are several reasons why a patient will have a frozen embryo transfer. They may be coming back for treatment after a successful IVF pregnancy, or because a fresh transfer was not successful. And in some cases a doctor will decide to do a ‘freeze-all’ cycle for medical reasons – usually due to the risk of a condition known as OHSS (ovarian hyperstimulation syndrome) where the ovaries essentially ‘over-react’ to the hormones used in a stimulated IVF cycle.
Another set of patients who require frozen transfers are those where genetic testing is carried out – either to screen embryos for a known inherited disorder or to carry out a full chromosome count prior to transfer.
So, the question became, if our results from frozen embryo transfers for these patients are exceeding our expectations in terms of pregnancy and healthy births, what can we learn that might be of advantage to all IVF patients?
The hypothesis that is now being rigorously tested at Genea is – does transferring a fresh embryo actually compromise the chance of success? In other words, is there an advantage to freezing all embryos?
The answer to this question could lead to a major re-think of the way we provide IVF worldwide.
A trial is now underway to compare the results of two groups of patients – 100 of whom will have the traditional fresh transfer and 100 of whom will have a freeze-all cycle.
The patients on the freeze-all cycles will have all embryos frozen and then have one transferred during their next natural cycle.
The theory being tested by the EVA (Elective vitrification of All embryos) trial is that the advantage seen from frozen embryo transfer may be due to the more natural environment in the uterus. In other words, that transferring an embryo at the appropriate point in a normal menstrual cycle gives a better chance of success than expecting an embryo to implant into the lining of the uterus immediately after the hormone stimulation required during IVF.
It may well be concluded that the best and quickest way to achieve a healthy baby may be from transferring a single frozen and thawed embryo.