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An analysis of 13,000 IVF pregnancies suggested the freezing process might be better for the mother and the baby’s health. It reported a lower chance of haemorrhage, premature birth and deaths in the first few weeks of life.
Dr. Allan Pacey, Fertility Expert at the University of Sheffield and Chairman of the British Fertility Society, said:
“This is an interesting and reassuring analysis about the outcomes for mothers and babies in pregnancies established following the transfer of frozen embryos created by in vitro fertilisation. Although we have been freezing embryos since the mid 1980’s, there have previously been scare stories from time to time questioning whether or not this was a good idea. Following the move to elective single embryo transfer in as many IVF cycles as possible, embryo freezing has recently become increasingly important. Therefore, this study is very timely in reassuring us that the outcomes of pregnancies from frozen embryos are associated with no increased risk and are arguably safer than pregnancies established using fresh (unfrozen) embryos. This is good news.”
Mr Stuart Lavery, Consultant Gynaecologist, Director IVF Hammersmith, said:
“1. This is an important paper as it provides reassurance about the perinatal outcomes following frozen embryo replacement cycles
2. It would be incorrect to conclude from these findings that we should stop performing fresh transfers and freeze all embryos with subsequent thaw transfers
3. The heterogeneity in this paper is significant: the pharmacological and endocrine environment will differ significantly in the frozen cycles (natural or drug assisted) and in the fresh (protocol and stimulation dose).
4. Only patients who have shown a ‘good’ ovarian response will have significant numbers of embryos to cryopreserve- they therefore should only be compared with fresh cycles where enough embryos were available to cryopreserve.”
Alison Murdoch, Head of Newcastle Fertility Centre at Life, Newcastle University, said:
“The study was designed initially to address unanswered questions about the outcome for frozen/thawed embryo pregnancies. There were concerns that freezing would have a detrimental effect. Therefore this is an encouraging study that provides some evidence that the pregnancy and early outcome for babies may be better after embryos have been frozen. The results of individual studies that are considered in this metanalysis are already being discussed in clinics and it is of some concern that conclusions have been drawn, incorrectly, are that we should routinely freeze all embryos and transfer them in a future menstrual cycle. I suspect that the media may pick up this message as the press release tends to promote this view even though the authors have cautioned against it in the paper. There is ample evidence to show that this would result in fewer pregnancies even if the outcome for those pregnancies were better.”
Further comment from Alison Murdoch: “The finding of improved results has raised more questions than it has answered. Does the lining of the womb respond better to the embryo in a subsequent treatment without stimulating drugs? Should we review the timing of transfer relative to the phase of the lining of the womb? Should we use drugs to stimulate the lining of the womb before transferring thawed embryos? Will the newer method of vitrification rather than slow freezing have different outcomes? Will the outcome for thawed blastocysts be different from early stage embryos? The paper demonstrated that the evidence so far is not able to provide answers to these questions. “The authors rightly draw attention to the limitations of the studies reported and the conclusions that can be drawn for the metanalysis. Most important is that the studies do not relate to ‘sibling’ embryos. Thousands of women will have had babies after transfer of embryos that were created at the same time but transferred at different times. If there is any value in the national database held by the HFEA, it must be in circumstances such as this. Information is submitted about every embryo created, transferred and every resulting pregnancy. This data must be analysed carefully and appropriately followed up as indicated before any changes to clinical practice are advised. This is potentially topical because of the debate about the future of the HFEA and their database. There were 1618 births in the UK after transfer of frozen embryos in 2008. Since about 40% of women who had frozen embryos will have conceived when the sibling embryos were transferred, there will be an adequate number of births in the UK to answer some of the questions raised in this paper. This is why we must have a national database that can be readily accessed for analysis. Did the authors ask to analyse the HFEA database and , if so, what was the outcome?”
Peter Braude, Emeritus Professor of Obstetrics and Gynaecology, Division of Women’s Health , King’s College London, said:
“The results of this analysis are counterintuitive since ‘second best’ embryos are generally selected for storage, and are then subjected to freezing and thawing procedures each of which carries risk. Albeit that the findings are difficult to explain, they are important in that they provide reassurance for cryopreservation programmes about short term outcome.
“Since these results only apply to those few embryos that result in successful pregnancy, one might speculate that only the most resilient embryos withstand the further insult and hence their immediate outcome is better. However information about long-term outcome for the children following freezing and thawing is lacking.
“Not all units in the UK pay sufficient attention to the importance of good cryopreservation and this study may stimulate improvement to the benefit patients.”
Dr Alan Thornhill, Scientific Director, The London Bridge Fertility, Gynaecology and Genetics Centre, said:
“1. Apples and oranges always difficult to compare.
2. Encouraging for cryopreservation and should reinforce the idea that it is at least no less safe than fresh IVF.
3. Good cryopreservation programme supports single embryo transfer strategies.
“As for should FET replace fresh transfers… jury is still out… but this is encouraging and we are likely to see more data coming out of Japan in which some large centres perform blastocyst vitrification and exclusive FET. This is made for a great multicentre RCT but I suspect reluctance on the part of some practitioners perhaps fuelled by a patient reticence. The way IVF is run now, it is hard to see the paradigm shift from ‘I have paid my money I want a fresh embryo transfer’ to one of delayed gratification.”