Dr. Jim Catt, Embryology director of Sydney IVF, Australia, and his colleagues have conducted the first study looking at cumulative pregnancy and live birth rates that took into account the transfer of previously frozen as well as fresh embryos. In 382 IVF patients aged under 38, who had at least two five-day-old embryos that were suitable for transfer or freezing, the cumulative live birth rate was exactly the same whether one or two embryos had been transferred in the first cycle.
Women who chose to have two embryos transferred in one cycle had a higher chance of success first time round – their live birth rate was 50% as opposed to 36% among the women who chose to have a single embryo transferred. But when the previously frozen embryos were subsequently transferred to the women who had failed to become pregnant in the first cycle, the cumulative live birth rates for both groups of women was 60%.
In addition, single embryo transfer (SET) carried fewer risks to mothers and foetuses. Among the 107 women out of 382 who chose to have SET, only three sets of twins from the subsequent frozen embryo transfers were delivered, while amongst the 275 women who chose to have two embryos transferred there were 90 twin pregnancies, four of which resulted in miscarriages with the loss of both twins and 18 of which resulted in the loss of one twin. The live birth rate per embryo transfer amongst the SET group was 36%, and 35% in the group choosing to have dual embryo transfer.
Dr. Catt said: "This is the first time that a study of cumulative pregnancy and live birth rates with five-day-old SET embryos has been conducted. Under the conditions of this study, twin pregnancies can be reduced drastically without compromising a patient's chance of a successful pregnancy. All patients younger than 38 are now offered SET and approximately 70% of them accept, with an acceptable ongoing pregnancy rate of 40%.
"For this particular study all patients were younger than 38 in order to avoid complicating the analysis with the well known effect of age on pregnancy rates. But transferring two embryos to patients over the age of 38 still carries a substantial risk of twins."
Abstract no: O-015 (Monday, 10.00hrs CET, Madrid room)
Note: A pregnancy rate of 40% after IVF compares well with pregnancy rates in the normal, healthy population of about 25% per cycle.
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