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 the University of Pennsylvania in Philadelphia, found that babies born from fresh embryos were 51% more likely to have low birthweight and were 15% more likely to die around the time of birth than those born from frozen embryos.
All the studies were presented today at the American Society for Reproductive Medicine conference in San Francisco.
In the UK, the National Institute for Health and Clinical Excellence (Nice) recommends that NHS trusts allow women three free cycles of IVF on the NHS.
It states that one cycle counts as the transfer of fresh embryos as well as any left over which have been frozen, in order to achieve a pregnancy.
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.
In the abstract for their study, the Australian authors said the findings suggested IVF techniques were not to blame.
“The adverse effects must operate via the woman,” they said.
“If these involve ovarian stimulation or anesthesia for oocyte (egg) collection, they may be able to be modified to improve birth outcomes.
“The other implication is that frozen embryo transfer should be more widely used.”
Dr Allan Pacey, fertility expert from the University of Sheffield 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.
“In an IVF cycle, the endometrium looks normal on ultrasound, but perhaps there is something subtle going on.
“Frozen embryo transfers are not as successful as fresh ones in terms of getting a pregnancy.
“So it may be that we have to balance the health of children against chances of success.”