Babies 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 in-vitro fertilization 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 in-vitro fertilization.

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.

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