Single embryo transfer (SET) reduces the risk of death within a month of birth for babies conceived via IVF, according to an Australian study. Results from a study of 50,258 births following IVF or ICSI, recorded in the Australian and New Zealand Assisted Reproduction Technology Database between 2004 and 2008, were presented at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Istanbul, Turkey.
'The number of embryos transferred per procedure is the major determinant of multiple pregnancy and multiple delivery, which contribute to an elevated risk of preterm birth and low birth weight, and its sequelae', said study leader Professor Elizabeth Sullivan from the University of New South Wales in Sydney, Australia. 'These are risks in addition to those already faced by women being treated for infertility'.
Births following the transfer of two embryos had a higher mortality rate than births following SET (19.1 per 1,000 births and 13.2 per 1,000 births). This difference was especially apparent in births following the transfer of fresh (as distinct from frozen) embryos - births involving two fresh embryos had a 74 percent higher risk of being stillborn or dying within a month of birth than births following fresh single transfers. Overall, the chance of a baby being stillborn or dying within a month of birth was 16.2 per 1,000 births.
Even when only one embryo implanted to form a continuing pregnancy, the chance of death before or soon after birth was 26 percent higher if another embryo was transferred at the same time. Professor Peter Illingworth, medical director of IVF Australia and a co-investigator on the study, explained it was possible that the failure of one embryo to implant properly could cause inflammation in the uterus that could affect the health of a surviving fetus many months later. But he cautioned that it was also possible the double embryo recipients might include more women who were smokers or overweight - both of which increase the chance of fetal and infant death.
In Australia, doctors already recommend SET in most cases for women under age 35. But until now, this has been with a view to avoiding twin pregnancies - which raise the risk of miscarriage, stillbirth and other complications.
Professor Sullivan said the findings showed that Australia's policy of promoting SET had helped to reduce infant mortality rates. 'Australia and New Zealand have shown that in the right policy environment a voluntary change to SET practice is achievable'. She added, 'there is justification for advocating SET as first line management in assisted reproduction with the aim of minimising preventable perinatal deaths'.
The proportion of single embryo transfers in Australia and New Zealand rose from around 14 percent in 1999 to just over 67 percent in 2008, an increase which was accompanied by a decline in multiple deliveries from around 22 percent in 2000 to around 8 percent in 2008.
Countries such as the USA and the UK have rates of SET of between 12 and 15 percent, compared with 70 percent in Australia. According to ESHRE, around one-quarter of IVF or ICSI cycles performed in Europe are single embryo transfers.
Professor Michael Chapman, from the University of New South Wales, said the study supported other research which showed that babies born after SET were 'bigger, less premature and have lower abnormality rates'.
'Compared with babies who were born after a double embryo transfer, the [SET] babies fared much better in terms of birth weight, in terms of stillbirth, in terms of complications of pregnancy', Professor Chapman said.