Freezing embryos after IVF does not boost the chances of becoming pregnant, a major trial has revealed.
Women undergoing IVF usually have a fresh embryo transferred into the uterus within a week of eggs being retrieved, with any ‘spare’ embryos frozen for use at a later date.
But in recent years some clinics have switched to a ‘freeze-all’ strategy, believing that it gives women’s bodies more time to recover from the disruptive hormonal treatment.
However, new research has found there is no benefit to using frozen embryos over fresh ones — with pregnancy rates around the same.
The study, published in the British Medical Journal, said that IVF clinics should avoid ‘freeze-all’ strategies and that fresh transfers should remain the ‘gold standard’.
Latest figures from the Human Fertilisation and Embryo Authority show that frozen embryos are now used in one third of IVF cycles in the UK, and their use has almost doubled in five years.
Some of this increase is because freezing embryos allows women to delay pregnancy until a date of their choosing.
But it also reflects suggestions from scientists that freezing all embryos would improve success rates as women would have more time to recover from IVF medication and invasive egg collection procedures.
Freezing embryos after IVF does not boost chances of becoming pregnant, a major trial has revealed (stock picture)
A clinical trial, on 460 women in Denmark, Sweden and Spain, set out to establish whether there are benefits to this approach.
The women were aged between 18 and 39. Half underwent treatment with fresh embryos, and the other half had frozen embryos.
FROZEN EMBRYOS: THE FACTS
Often in IVF, women have good quality embryos leftover which they can’t use.
Instead of discarding them, they have the option to freeze them to use in the future.
Not all embryos are suitable for freezing so only good quality embryos will be chosen to freeze.
Embryos can be frozen at different stages of their development – when they’re just a single cell, at the two to eight cell stage or later in their development – the blastocyst stage.
The embryos will be put in a special substance, which replaces water in their cells.
This will protect the embryos from damage caused by ice crystals forming.
They’ll then be frozen, either by cooling them slowly or fast freezing (vitrification) and stored in tanks of liquid nitrogen until you’re ready to use them.
After their eggs were collected and mixed with sperm in a laboratory, the fertilised eggs are left to continue to grow in a laboratory for a number of days.
For those having a fresh embryo transfer, the embryos were transferred into the womb a few days after the eggs are collected.
In the frozen embryo group, the newly formed embryos were frozen and thawed out at least a month later before being transferred.
The women were then followed up to see whether they had fallen pregnant.
The authors found that pregnancy rates did not significantly differ between the groups — 27.8 per cent of those who froze their embryos fell pregnant compared with 29.6 per cent who had a fresh transfer.
And no significant difference was found between the live birth rates between the two different groups.
The authors, led by researchers from Hvidovre University Hospital in Copenhagen, Denmark, wrote: ‘The findings warrant caution in the indiscriminate application of a freeze-all strategy when no apparent risk of ovarian hyperstimulation syndrome is present.’
They added that ‘a safe fresh embryo transfer strategy can be applied to women with regular menstrual cycles’ but cautioned that those who become at risk of ovarian hyperstimulation should have their embryos frozen to avoid risk of the condition.
Ovarian hyperstimulation syndrome is a rare complication of IVF.
It occurs in women who are very sensitive to the fertility medication taken to increase egg production.
Too many eggs develop in the ovaries, which become very large and painful.
How does IVF work?
In-vitro fertilisation, known as IVF, is a medical procedure in which a woman has an already-fertilised egg inserted into her womb to become pregnant.
It is used when couples are unable to conceive naturally, and a sperm and egg are removed from their bodies and combined in a laboratory before the embryo is inserted into the woman.
Once the embryo is in the womb, the pregnancy should continue as normal.
The procedure can be done using eggs and sperm from a couple or those from donors.
Guidelines from the National Institute for Health and Care Excellence (NICE) recommends that IVF should be offered on the NHS to women under 43 who have been trying to conceive through regular unprotected sex for two years.
People can also pay for IVF privately, which costs an average of £3,348 for a single cycle, according to figures published in January 2018, and there is no guarantee of success.
The NHS says success rates for women under 35 are about 29 per cent, with the chance of a successful cycle reducing as they age.
Around eight million babies are thought to have been born due to IVF since the first ever case, British woman Louise Brown, was born in 1978.
Chances of success
The success rate of IVF depends on the age of the woman undergoing treatment, as well as the cause of the infertility (if it’s known).
Younger women are more likely to have a successful pregnancy.
IVF isn’t usually recommended for women over the age of 42 because the chances of a successful pregnancy are thought to be too low.
Between 2014 and 2016 the percentage of IVF treatments that resulted in a live birth was:
29 per cent for women under 35
23 per cent for women aged 35 to 37
15 per cent for women aged 38 to 39
9 per cent for women aged 40 to 42
3 per cent for women aged 43 to 44
2 per cent for women aged over 44