Previous work suggested that frozen embryos in IVF were more successful than fresh ones in women with polycystic ovary syndrome (PCOS) who were 'anovulatory', that is, their bodies did not release an egg every menstrual cycle.
To see if the same was true in women without PCOS who ovulated normally, studies conducted in China and Vietnam, randomly assigned IVF patients to a fresh embryo transfer or a frozen embryo transfer cycle, and then recorded the pregnancy and live birth rates of the groups. The studies are published in the New England Journal of Medicine.
Both studies showed similar pregnancy and live birth rates for fresh and frozen embryos, with about one-third of the IVF transfers resulting in a live birth in the Vietnam study, and half resulting in a baby in the China study.
The studies also found no difference in the occurrence of neonatal and obstetric complications between the two groups. Although, frozen cycles were associated with lower rates of OHSS (Ovarian Hyperstimulation Syndrome) (0.6 percent frozen versus 2 percent fresh).
Dr Lan Vuong, lead author of the Vietnamese study, at the University of Medicine and Pharmacy at Ho Chi Minh City, said: 'Frozen embryo techniques are growing in popularity in fertility clinics worldwide. This is one of the reasons why our research is important for fertility clinicians and researchers, and of course couples who are hoping to have a child.'
She also added that the results 'should transform the way [IVF] is practised. After the first fresh embryo transfer, it will be possible to freeze the remaining embryos and transfer them one by one, if necessary, without reducing the chance of pregnancy.'
Professor Ben Mol at the University of Adelaide in Australia, and a co-author on the Vietnamese paper, addressed cost concerns: 'Couples concerned about such unnecessary costs of freezing all embryos do not need to go down that path, and will still have the same live birth success rate.' This statement was supported by Dr Vuong who conducted a cost-effectiveness analysis of the two types of transfers and found that 'freezing embryos and subsequent transfer is not cost-effective over fresh transfer'.
Dr Christos Coutifaris at the University of Pennsylvania’s Perelman School of Medicine in Philadelphia, who was not involved in the research, told Reuters Health that the findings for PCOS patients should not be applied to ovulatory women.
'Two papers, equally large and done in non-PCOS patients, show that in terms of live birth, which is what we care about, there is no difference…so to apply the rule to everybody that we should freeze your embryos is probably not correct,’ he said.