that fresh is always better and used as a first choice," Dr Maheshwari said. "Initially there were concerns about the safety of freezing techniques, and it was felt the quality of the embryo could deteriorate and impact on the health of the child. However, data to date has been reassuring," he told the British Science Festival in Aberdeen. Current practice for most IVF clinics is that the best, fresh embryos are used first and only spare, good-quality embryos are frozen for transfer at a later stage. Freezing embryos has become more popular since single embryos have been transferred, rather than the riskier transfer of two or more embryos. But Professor Alison Murdoch, head of the Newcastle Fertility Centre, said the findings of the review did not justify a change in existing policy. "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," she said. Peter Braude, a fertility specialist at King's College London, said the results of the study were counter-intuitive since "second-best" embryos are usually selected for freezing, with the best being transferred immediately.