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24 June 2019
Freezing embryos may not improve IVF success ratesBSIP/Universal Images Group via Getty
By Clare WilsonA commonly used fertility medicine technique of freezing embryos and waiting several weeks before using them is ineffective at boosting pregnancy rates, a trial has shown.
The approach is growing in popularity, and in the US about a quarter of IVF cycles now use this “freeze-all” strategy, although this includes women who need it for health reasons.
During standard IVF, women take medicines to encourage their ovaries to produce several eggs, which are then collected and fertilised with sperm in a dish. Any embryos are allowed to grow for a few days before one or two are transferred into the uterus in the hope one will implant and lead to pregnancy. Any spare embryos are frozen for future attempts.
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To freeze…
But fertility clinics are increasingly recommending that women freeze all their embryos and wait several weeks before implanting the first ones. The thinking is that this may raise the chances of pregnancy, because if an embryo is transferred straight away, the lining of the uterus may be less receptive due to the medicines women take to produce multiple eggs.
Now a trial has put this idea to the test by randomising 460 women at clinics in Denmark, Sweden and Spain to either the freeze-all approach or the standard method of transferring one unfrozen embryo straight away.
Freezing all the embryos led to a 26 per cent pregnancy rate compared with 29 per cent for the standard method. This was such a small difference it could have arisen due to chance – but it does suggest freezing offers no advantage. The research was presented at the European Society of Human Reproduction and Embryology in Vienna today.
There have been three previous trials looking at this question, only one of which found any benefit.
…or not to freeze
“I think that’s sufficient evidence there is no benefit from a freeze-all strategy,” Sacha Stormlund of Copenhagen University Hospital in Denmark.
Implanting an unfrozen embryo straight away means there is no delay. “Women are usually anxious to get pregnant as soon as possible,” says Stormlund.
The exception is women who seem to be at risk of a side-effect of IVF called ovarian hyperstimulation syndrome, which can lead to blood clots. Here the best course is to wait an extra two months to let hormone levels return to normal, says Stormlund.
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