Transferring one IVF embryo, followed by a second, frozen-thawed embryo if the first fails to implant, is almost as likely to result in a pregnancy as transferring two at a time - in women under 35, Swedish researchers report. Team leader Christina Bergh, based at the Sahlgrenska University Hospital, says that the benefit of the approach is 'the dramatic decrease in multiple birth rate with no substantial reduction in the overall live birth rate'. The findings are published in the latest issue of the New England Journal of Medicine.
In recognition of the health risks associated with multiple births, for both women and children, several countries have legislation or guidelines that limit the number of embryos that can be transferred to the womb following IVF treatment. In 1993, Swedish IVF doctors started to reduce the number of embryos transferred into a woman from three to two. For the latest study, 661 women under the age of 36 with at least two good quality embryos were randomly assigned into two groups. In the first group, the women underwent a transfer of two fresh embryos, while in the second, just one embryo was transferred. Doctors then transferred a second, frozen-thawed embryo, if the first did not result in a pregnancy.
The results showed that the single embryo transfer method resulted in a similar live birth rate to the two embryo group. In the two fresh embryo group, 142 of 331 (42.9 per cent) women had pregnancies resulting in at least one live birth, whereas in the second group, 128 of 330 women (38.8 per cent) had one live birth. 27 per cent of the second group became pregnant after a single embryo transfer, while the rest had to have a second embryo transferred.
'IVF has come a long way since the early days when you would put in four embryos and have a 15 per cent success rate', said Owen K Davies, author of an editorial that accompanies the new study. 'Now that each embryo has a better chance of implanting than they used to, we have the luxury of worrying about multiple births', he added. However, he also stressed that the women taking part in the study were likely to become pregnant through IVF - their average age was 31, it was only their first or second attempt at IVF, and each had at least two viable embryos. In the US, said Davies, unlike Sweden and other European countries, 'patients go to IVF as the last resort', so their average age tends to be much older. He also pointed out that only 50-75 per cent of embryos survive the freeze-thawing process, so that 17 per cent of the women in the study did not have the option of a second embryo transfer.
US infertility specialist Eric Surrey says that it is increasingly clear that for patients with a good chance of conception, single embryo transfer may be preferable to multiple transfers. However, he points out that in the US, 'insurance almost never pays for IVF, so maximising the chances of pregnancy the first time around is a big concern'. He also says that couples who don't have children often see twins as 'a desirable outcome', seeing it as 'two for the price of one'. Davies says that the vast majority of twins do 'just fine', but the risk is considerably higher than for single birth pregnancies. 'Having babies one at a time is safest', he said.