Using stored embryos cuts the risk of bleeding in pregnancy, premature birth, and giving birth to an underweight baby by almost one third, a study has found.
The risk of a baby dying around the time of birth is also reduced by a fifth.
Scientists made the discovery after analysing data from 11 international studies involving more than 37,000 IVF pregnancies.
In some cases, newly conceived fresh embryos were used. In others, embryos that had been frozen and stored for two to three months were implanted.
Standard practice is to choose the best embryos for fresh transfer, and only freeze those of good enough quality that are spare.
However, the new results suggest it might be wise to freeze all embryos.
Dr Abha Maheshwari, senior lecturer at the University of Aberdeen, said: “We found pregnancies arising from the transfer of frozen thawed embryos seem to have better outcomes both for mums and babies when compared to those after fresh embryo transfer.
“If pregnancy rates are equal and outcome 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.
“This represents a major paradigm change in assisted reproduction, and one which could satisfy the twin demands of optimising safety and success.”
Dr Maheshwari presented her findings at the British Science Festival, which opened yesterday at the University of Aberdeen.
The scientists think there could be two reasons for the results. One is that only prime quality embryos are likely to survive the freezing process. The other, more popular theory is that the womb lining is allowed time to settle and recover from the rigours of IVF hormone treatment.
A pregnancy too soon after a women is given fertility-boosting drugs is known to increase the risk of hyperstimulation.