Freezing embryos after IVF does NOT boost the chances of becoming pregnant

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.

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.

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.