IVF babies born from frozen embryos are healthier than those that develop from fresh embryos, according to research out today.

IVF babies born from frozen embryos are healthier than those that develop from fresh embryos, according to research out today.

Freezing embryos resulted in babies that were less likely to die or be premature and they had a more normal birthweight, according to three separate studies.

One study from Finland found that babies born from fresh embryos were 35% more likely to be premature and 64% more likely to have low birthweight than those born from frozen.

A second study, from Pennsylvania University in Philadelphia, found that babies born from fresh embryos were 51% more likely to have low birth weight and were 15% more likely to die around the time of birth than those born from frozen embryos.

All the studies were presented at the American Society for Reproductive Medicine conference in San Francisco.

UK success rates using frozen embryos are generally lower than for fresh.

Women under 35 using fresh embryos have a 31% chance of getting pregnant per IVF cycle, compared with a 20.1% chance for those of the same age using frozen embryos.

Among women of all ages, the figures are 24.4% and 17.4% respectively.

Today's third study, led by experts at the Royal Women's Hospital in Melbourne, Australia, found 11% of babies born from fresh embryos had low birthweight compared with 6.5% of babies born from frozen. A total of 12.3% of babies born from fresh embryos were premature, compared with 9.4% of those born from frozen, while 1.9% also suffered death compared with 1.2% from frozen.

Dr Allan Pacey, fertility expert from Sheffield University and secretary of the British Fertility Society, said the formation of the placenta could play a role in explaining the results but the effect was as yet unknown.

"This may be a bit of biology that has escaped most people," he said. "The assumption has always been that if the endometrium is thick, it's functional," he said.

"In an IVF cycle, the endometrium looks normal on ultrasound, but perhaps there is something subtle going on."