Frozen embryos better in IVF?Comment on this story
London - Women having fertility treatment might get better results by putting their embryos on ice, doctors say.
Normally in IVF, the embryos thought to have the best chance of resulting in a pregnancy are used in treatment a few days after they are made in a dish.
Any that are left over can be frozen to allow the woman to try again if the treatment isn’t successful or to add to her family in the future.
But there is growing evidence that it may be better for women having IVF – and their babies – if all embryos are frozen first.
A review of 11 studies from around the world, involving more than 37,000 pregnancies, found frozen embryos to be safer for mother and child.
Babies were around a third less likely to be born small or premature and 20 percent less likely to die in the first days or weeks after birth.
Women who used frozen embryos were around a third less likely to suffer complications such as bleeding in pregnancy than those who used “fresh” ones.
Researcher Abha Maheshwari, an IVF consultant with NHS Grampian, said her results should help to allay fears about the safety of freezing something as delicate as an embyro.
But they are counter-intuitive, as doctors try to pick the highest-quality embryos for immediate use and freeze those deemed second best.
Dr Maheshwari told the British Science Festival in Aberdeen: “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.
“Traditionally, it has been thought that fresh is always better and used as a first choice.”
It is not clear what is behind the results but it may be that only the strongest embryos survive being frozen for several months.
The delay caused by freezing may also give the woman’s body – including the delicate lining of her womb – time to recover from the powerful drugs given at the start of IVF treatment to boost egg production.
Lengthening the time between administering the drugs and pregnancy should also cut the odds of a woman suffering ovarian hyperstimulation syndrome, a potentially fatal complication that can be triggered by fertility medication.
Other studies suggest a woman is roughly as likely to become pregnant from a frozen embryo as a fresh one.
But Dr Maheshwari said more research needed to be done before clinics were advised to freeze all embryos as a matter of course.
Factors to take into consideration include some hospitals being better at freezing than others. In addition, some women’s embryos may simply not survive the cyropreservation, or freezing, process.
Peter Braude, emeritus professor of women’s health at King’s College London, said the findings “are important in that they provide reassurance for cryopreservation programmes about short-term outcome”. - Daily Mail