The findings discourage the 'freeze-all' strategy adopted by some fertility clinics in recent years. They thought that using frozen embryos rather than immediately transferring fresh embryos to the uterus allows patients' bodies more time to recover from disruptive hormonal treatment required in IVF and intracytoplasmic sperm injection (ICSI) cycles.
Preliminary results of the randomised, multi-centre trial were reported last year at the European Society for Human Reproduction and Embryology's annual meeting (see BioNews 1003). Speaking at the meeting, lead author Dr Sacha Stormlund from Hvidovre University Hospital in Copenhagen, Denmark, remarked: 'I think we can now reasonably say, based on our results and those from other recent trials, that in normally ovulating patients there is no apparent benefit from a freeze-all strategy in IVF.'
The study, recently published in the British Medical Journal, analysed 460 IVF and ICSI patients across Denmark, Sweden and Spain. Participants were aged between 18 and 39, and receiving their first, second or third treatment cycle. Half of participants underwent frozen embryo transfer one month after initial egg harvest, whereas the other half received fresh embryo transfer a few days after harvest.
The researchers found that there was no significant difference between the percentage of women who fell pregnant in each treatment group, 27.8 percent for women who froze their embryos compared with 29.6 percent who underwent fresh embryo transfer. In addition, there was no significant difference between the live birth rates, 27.4 and 28.7 percent for frozen and fresh embryo transfer, respectively.
The study also reported a slightly increased risk of preterm birth in the fresh embryo transfer group. However, time to pregnancy was significantly longer in the frozen embryo transfer cohort, leading the authors to conclude that 'fresh embryo transfer should be used as the gold standard'.
The findings could influence best practice in fertility clinics and are especially relevant given the enormous rise in frozen embryo transfer cycles in recent years – the Human Fertilisation and Embryology Authority's (HFEAs) latest figures reported a 93 percent increase between 2013 and 2018.
The authors noted that fresh embryo transfer may not be appropriate for all patients, specifically those at a higher risk of the serious side effect of ovarian hyperstimulation syndrome (OHSS). In these patients, frozen embryo transfer can reduce the risk of OHSS.
Dr Stormlund's team concluded by recommending that: 'The findings warrant caution in the indiscriminate application of a freeze-all strategy when no apparent risk of ovarian hyperstimulation syndrome is present.'