Frozen embryos are more likely to produce successful, complication-free IVF pregnancies than those that are fresh, research has suggested.
Using stored embryos cuts the risk of bleeding in pregnancy, premature birth, and giving birth to an underweight baby by almost a third, a study has found.
The risk of a baby dying at around the time of birth is also reduced by about a fifth.
If the findings are confirmed it could have major implications for the public funding of In-Vitro Fertilisation treatment.
Currently the NHS regards embryo freezing as an extra service patients are expected to pay for themselves. If freezing becomes a routine part of IVF treatment there may be pressure to change this rule.
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. But the new results suggest it might be wise to freeze all embryos.
Dr Abha Maheshwari, senior lecturer at the University of Aberdeen and Consultant in Reproductive Medicine with NHS Grampian, 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 at the University of Aberdeen. The research also appears in the journal Fertility Sterility.