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Women who undergo fertility treatment using cryopreserved embryos may have healthier babies and fewer complications than those who use ‘fresh’ embryos, a study suggests.

A review of 11 studies comparing outcomes of more than 37,000 pregnancies following IVF showed that using embryos that had been cryopreserved reduced the chance of antepartum haemorrhage (vaginal bleeding during pregnancy), premature birth and low birth weight. The risk of perinatal mortality was also reduced, but the use of cryopreserved-thawed embryos appeared to increase the risk of caesarean section.

‘If pregnancy rates are equal and outcomes in pregnancies are better, our results question whether one should consider freezing all embryos and transfer them at a later date, rather than transferring fresh embryos’, said lead researcher Dr Abha Maheshwari from the University of Aberdeen.

Although in absolute terms the difference between the risks following fresh and cryopreserved embryo transfer were small and remain low, the findings could lead to a debate over the current practice for most fertility clinics of preferring to use fresh embryos to cryopreserved ones. ‘This represents a major paradigm change in assisted reproduction’, said Dr Maheshwari. ‘Traditionally it has been thought that fresh is always better and used as a first choice’.

Speaking at the British Science Festival in Aberdeen, Dr Maheshwari explained there had been concerns over the quality of cryopreserved embryos and the impact on the child’s health. ‘However, data to date has been reassuring’, he said.

The use of cryopreserved embryos results in fewer pregnancies overall, however. Alison Murdoch, professor of reproductive medicine at Newcastle University, said: ‘There is ample evidence to show that this would result in fewer pregnancies even if the outcome for those pregnancies were better’.

‘The results of individual studies that are considered in this meta-analysis are already being discussed in clinics and it is of some concern that conclusions have been drawn, incorrectly, that we should routinely freeze all embryos and transfer them in a future menstrual cycle’, Professor Murdoch added.

Stuart Lavery, director of IVF at Hammersmith Hospital in London, told BBC News it would be ‘incorrect to conclude from these findings that we should stop performing fresh transfers and freeze all embryos’. However, Lavery also said the study provided reassurance that cryopreserved embryos were as safe as fresh ones.

Commenting on the study, Dr Allan Pacey, chairman of the British Fertility Society, said: ‘What’s really useful is that it shows that from the point of view of the woman’s health during labour, and some early measures of the baby’s health, frozen embryos do all right and are arguably better’.