IVF babies born from embryos that are frozen and thawed are less likely to be underweight or premature than those conceived during fresh treatment cycles, research has shown.

The findings show that the use of frozen embryos could soon be accepted as completely safe, doctors said.

Another team of researchers told the European Society of Human Reproduction and Embryology conference in Barcelona that IVF success rates could be improved by as much as 15 per cent with a “viability index” for selecting embryos with the best chance of a healthy pregnancy.

The Danish study into frozen embryos found that the average birth weight of those babies was 200g more than in fresh-embryo IVF.

The findings, from a team led by Anja Pinborg, of the Copenhagen University Hospital, are important because women are increasingly encouraged to use one fresh embryo — to avoid multiple births — and to freeze any others produced in the process for later use.

Dr Pinborg said it was highly unlikely that freezing improved the health of embryos. The figures could be explained because patients who froze embryos were generally young women with a good prognosis. Poor quality embryos were also more likely to die during the thawing process.

“These findings are reassuring,” she told the European Society of Human Reproduction and Embryology conference in Barcelona. “If our results continue to be positive, frozen embryo replacement can be accepted as a completely safe procedure, which can be used even more frequently.”

Scientists from Yale University told the conference that overall IVF success rates could be improved by as much as 15 per cent by a new “fitness test” that can predict which IVF embryos will implant into the womb up to 70 per cent of the time.

The non-invasive procedure examines chemical fingerprints in the culture media in which they grow in the laboratory. Scientists said the technology, known as metabolomics, should be ready for widespread use within two to three years, and predicted that the viability index could become a routine part of fertility treatment.

Denny Sakkas, who is leading the research, said: “The other side of IVF is that we probably fail to get patients pregnant about two thirds of the time we do an embryo transfer. One of the reasons is we’re not that good at picking the best embryo we have available.

“In the clinic, we would probably be looking at a 10 to 15 per cent improvement in pregnancy rates.

“It’s not going to make a bad embryo good, but it should help us to tell them apart. This definitely could make the difference between people getting pregnant or not.”

The average success rate for IVF in Britain is 21.6 per cent across women of all ages, and 29.6 per cent for women under 35.

There is no evidence that acupuncture during IVF treatment does anything to improve women’s chances of having a baby, the most extensive review yet has concluded. Sesh Sunkara, who led the research at Guy’s and St Thomas’ Hospital in London, told the conference: “If women come to me and ask if they should have acupuncture, I have to say there is no evidence that it helps.” She said more trials were needed to settle the issue.

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